As of right now, there's no real need for it to ever change, besides, the only other perfect triangle is Flying/Rock/Fighting. Definitely not the most interesting trio of types, -.-;
That trio would work, but I agree that it does not seem very interesting because those types really have almost no relation to each other aside from being other options for a 'super effective/not very effective' triangle.
With
Fire/Water/Grass, they make a perfect triangle, with the first 2 commonly being seen in mythologies relating to the classical elements. In practically any story, if the main character/group or someone/-thing of the sort specializes in Fire, you can almost
guarantee that a Water person, group, monster, etc. will be present in some way, shape, or form. Grass (or "Wood") is also seen as a represented element in various mythologies, though not nearly as common as Fire/Water conflicts are. Furthermore, red, blue, and green are the primary colors of light, so that's another relation. Lastly, the original Generation I Pokemon games (
when you take in account the Japanese Pokemon Green Version as well) were represented by Fire/Water/Grass starters (
Red, Blue, and Green Versions), so that theme has virtually manifested as one of Pokemon's core attributes in subsequent games.
Pokemon Yellow Version and Pikachu deserve a mention as yellow replaces green in the primary colors of paint. In addition, from my experience, yellow tends to be utilized as a 4th addition when red, blue, green have already been featured in some sort of trio (i.e., at the Battle Tower entrance in RSE, a Pokeball is surrounded by red, blue, green, and yellow tabs) - the same for green being a 4th addition when a red-blue-yellow trio has been established instead. Thus, yellow can be seen relating to the common RBG triangle.
And yeah, even though
Fighting/Psychic/Dark does not make a perfect triangle, here is an excerpt of a post I wrote earlier on the matter of such a unique starter 'triangle'.
As a side-note, I'd still like to see a Dark/Psychic/Fighting trio. Yes, I know the triangle is partly broken, but the Psychic-type could be granted a unique ability that removes the Dark-type's immunity to Psychic-type allows the user to hit Dark-types for "not very effective..." or normal effectiveness (similar to the effect of the move Miracle Eye). However, 'normal effectiveness' would still break the "not very effective" triangle...
The reason I prefer this "trio" is that the Fighting and Psychic-types represent two parallels of combat (physical combat, and mental/telekinetic combat). Furthermore, the two "alignments" of combat are utilized (as in, Fighting-types fight with just and honorable tactics, as opposed to Dark-types that use sneaky and underhanded, dishonorable tactics...)
I actually came up with three Fakemon Starter Pokemon lines that formed a trio of Dark/Psychic/Fighting... For
Rule of Cool, the Fighting-type ended up as
Fighting/Dragon, the Psychic-type ended up as
Psychic/Poison with a Miracle Eye-esque ability to hit past Dark-type, and I
really debated with the combo for the last one (it's a
Dark-type, but the more prominent types I was debating on were
Steel-type/
Rock-type/Ice-type [allowed for a 4x weakness to Fighting-type, but I figured such combos would remind me too much of previous Pokemon made already] and
Ghost-type (served the Pokemon's appearance, but would worsen the triangle even more)...
Anyway, I think it would be cool if at least
one generation were able to deviate from the Fire/Water/Grass triangle of tradition, just to serve as a
one-time refreshing change of pace from past games. :D