I have to segment this because the the size.
Yes. I know the arguments about why there hasn't been one yet.
Dark types translate into evil when looked at in Japanese.
Dark types are usually used by the bad guys.
Gym leaders are supposed to be role models.
They're easily taken down. (Excuse me? Bug types?)
The gym matches town environment, and there hasn't been a town yet that would fit.
I really don't have anything to say about any of this. A lot of these points are usually brought up, but they weight only what we allow them to.
However, of all the games so far, I feel as if we might have a chance here. Sun and MOON! Moon, night, dark? And to take down those arguments listed above. And yes, this will all come together to relate to a gym leader theory:
First flaw I see in your synopsis. Moon = Dark. Unfortunately as of Generation 6 Moon = Fairy and Mystical. Moon hasn't ever been associated with Dark types canonically. Dusk and Night have, but Moon related moves were Normal based pre-Fairy and Fairy Type post Gen 6. We have a new Pokemon to represent the Moon and it is Psychic/Ghost, tying into two older Moon related Pokemon who are also Psychic. So the Moon has more connection with Psychic types and Fairy Types than it does Dark Type.
They're not evil. Dark types are more trickstery when you look at a lot of them. People often point to the move sets, but It makes me think of how in MMOs a lot of tanks seem to put down on us Stealth types for "hitting and then running off". Like somehow it's cowardly, but isn't running kinda the point here? Hit fast, run faster, wear them down, and don't die. Same with dark types. They play to their strengths and other pokemon's weaknesses. There's nothing really evil in that. More cunning. You want evil? Well...
Evil is different depending on culture and viewpoint. Trickstery design is inherently evil to a good portion of Asian culture. Sneaking about is considered cowardice and a sign that you are an evil person. Using underhanded tactics as well. Both of these paint you a someone who cannot fight fairly in typical Asian stories and anyone that fights using these methods is typically evil. Even Ninjas in Asian folklore are inherently evil.
If a dark type gym leader is bad, what about poison and ghosts? Anyone remember a certain ghost balloon that carried off little children in the night? What about Kanga, who was actually a member of team rocket in the manga? Fire could be pretty destructive.
Poison and Ghost aren't represented as Evil though. Poison is commonly used by evil teams just as Dark Types and Normal Types. Ghost gyms don't even give off evil vibes. Most of the time they are just gothic and creepy. Poison is a danger game. None of the Manga counterparts are Canon to the games either. Koga, Sabrina, and LT Surge aren't Rocket executives in the game, nor are they evil. Giovanni was the only bad guy gym leader and he left his Gym Closed for an indefinite amount of time until you thwarted all of his schemes and he took up his role again. The Manga also made the Elite 4 into evil people in the Yellow Saga as well as Pryce in the Johto set.
There have been many characters who are not evil with dark types. Gary had Umbreon, remember? Absol is actually a good pokemon that WARNS people about disaster. Darkrai, who is often seen as evil, has been shown as good in the movie. What about Zorua? Oh, and what about all the non dark types that have been shown as evil?
Gary isn't Canon to the games either. Blue, his gaming counterpart has only ever owned 1 Dark Type and that is Tyranitar after you've already beaten him as Champion and he gets a new team to fight you with as well as his HGSS Rematch team. He has it to replace his Rhydon. Absol is a social question. Most believe that Absol's presence it more danger than the event that will follow. It is an ominous warning because they are present when bad things happen. If they constantly appear where bad things happen, people start to believe that they are the actual cause of the events and fear them. You can't really argue for or against that an Absol is the cause of horrible events or if they are just drawn to the sight of these events. Either way, seeing one is never a good sign to those that live in that kind of world. This is taking superstition to a very high level but in their world, it has accurate negative results. Using Movies where they paint the Pokemon in a misundertood light is also a bad representation. That Darkrai was benevolent but they aren't all like that. The game event has Darkrai plaguing a child with nightmares. There was no threat from the child, but Darkrai put the child to sleep and let it succumb to nightmares until the Player cured the child. Zorua are mischievous. Even the movie highlighted this. The anime did as well. They'd prefer to be left alone, but still love to prank other. While they are somewhat harmless, they can cause harm with their pranks.
This is stated many times in the Anime and Games, A Pokemon cannot truly be evil. They only follow the orders of their masters. Outside of ownership, Pokemon do what they must to survive. Like Florges running amuck with Bug Types in the swamp and driving out the inhabitants (though this was also Team Rocket's doing). You also have Pokemon like Ursaring who get jealous of other Pokemon like Hawlucha and try to get revenge their own way. Some are bullies. Some are mean and very territorial. None are realistically evil. We can't use individual merits to dictate or counteract lore and other sources. Some are more malevolent. Some are more benevolent. Some are seen as evil due to superstition and happenstance.
Driftloon, since it was mentioned earlier, is another like Absol. Bad things happen so it is believed they are the cause. Children holding onto a Driftloon go missing is the general story along with they are made from spirits of people and Pokemon. A common story about Spirits is how they tend to steal children away, a very common one is about a dead mother who lost her child and steals any child that comes close to her domain. She doesn't steal them to be evil, but because she is lonely and her motherly instincts drive her to protect the children she steals. Driftloon have a common build up. They are made of spirits of People and Pokemon. Two things that love to be with others, especially children. Spirits are known to be lonely and seek others to fill in the loneliness. They aren't Malevolent when they take them.
Again...bug types might be the easiest to take down. We have gyms with those. Dark types are actually pretty strong when raised right. There are tons that are type mixes, which means not only extra weaknesses, but extra strengths!
Bug types are also more common and are more fitting as a stepping stone that Gyms are supposed to represent. Even with the newer cases of early bug type Gyms. Thematically, Dark types don't fit in with this ideal. They are more final boss level which is perfect for them to be E4 and Champion/Main Bad guy Pokemon.
What about the ones with the ghost gyms? Or how about one that's known to be in a "bad part of the region"?
There is no such thing as "bad part of the region" in any Pokemon game.
All kinds of potential that shatters the "it can't happen because reasons listed above". It fits the "moon" bit. People have been talking about it for a while...what do you think? I'd love for this to happen, ESPECIALLY if they're not evil. I'm really tired of that being associated with my favorite type...we must end the pokemon typism once and for all. My Houndoom must be insulted no longer.
Again, Dark types don't fit the moon bit. Moon is predominantly Psychic and Fairy Type. Pokemon representing the Moon are all Psychic type. The only two existing "Moon" based attacks thus far are both Fairy type. Pokemon that are directly linked to the Moon are Psychic and Fairy typed as well.
None of this can be used for or against a Dark Type Gym however. The only thing that will indicate a Dark Type Gym's existence is GameFreak wanting to make one. Everything else we use to argue either way is pure conjecture.
How I personally feel upon the matter. I'd love a Dark Type Gym, but at the same time I feel that belittles the type. It's in a place of prominence being mostly E4 or Final Boss like with the evil teams. I'd rather see a Champion who specializes in Dark Types than a Dark Type Gym. A Gym is battle and done. E4 and the Champion can be battled many times and are more likely to change with additional encounters than Gyms are. There are so many wrongs that can happen if they are made into a Gym, being forgetfully easy and early or being laughably easy and late, having a bad connection to correlate the Gym to the story and or location, or giving the Gym Leader limited choices (which we'll pretty much get regardless)
No matter what outcome we receive someone isn't going to like how it's done when it'd finally done. It's one of the types, I'd rather not see put in a bad set up just for the sake of having it as a Gym.
You're really overanalyzing this. There's been a Dark-type E4 before, so a Dark-type gym isn't really impossible to imagine, it's just whether or not GameFreak cares to make one.
Really, this sums it up.
Maybe, but the Elite Four are so detached from the rest of the region. Not to mention two of those elite Four were members of evil teams in the manga, and the other looks like Dracula. His name is basically devil. So that doesn't earn many points. :/
And that's why they'd be gym eight.
Believe it or not, GF actually does do a lot of things that aren't so straightforward as "it's just there". Not to mention various things from the anime, manga, and games that point in a certain direction. They like their easter eggs too. If I was part of the game making process, you better believe there'd be tons of stuff, and there is if you look.
Gamefreak has no direct relationship to the Manga or the Anime hence why non of what occurs in either is Canon to the main games. GF also doesn't control every game, just the core ones. So changes made in PMD, Colosseum and XD, and the Ranger series are all independent and have no canon tie ins with the core sets. TPCi oversees the Amine and Movies, and a different group oversees the Manga. Manga group rarely ever works under the anime or game groups which is why they have such drastic differences.