"Gamefreak even said only reason it exists is because they wanted something to be stronger than Dragons" No they didn't. It wasn't "Here's a new type solely introduce to balance out Dragons, the Fairy type". Also, if that's the only reason they introduced this type, then why Fairy? If the only reason they introduced a new type was to balance dragons, then it could have been a different type entirely. You honestly think GameFreak would make the new type "Fairy" just for the sake of it? No. They obviously used Fairy intentially because it fits.
Ya it was asked at E3 why Fairy existed.
Q - Will there be a story reason why Fairy-type will all of a sudden exist?
A - When we first decided we wanted to bring the type into the world, we wanted to find a way to balance the stength of the Dragon type. But no one wants us to weaken the Dragon-type Pokemon, so we decided to come up with something that could go against a Dragon, so that's why we came up with the Fairy-type.
They asked to explain why Fairy existed in the game. Their answer, we wanted to weaken Dragon without actually changing their stats so we created a new type to balance Dragon out more. The entire discussion was about adding a new weakness to Dragon Types so they made Fairy Type. Fairy Type exists to directly combat Dragon types. That was their purpose of being created.
And don't give me the whole "dragons are imperious to magic". In most fairy tales the only way to defeat the dragon is to use magic-based weapons. This is evident in SO many japanese stories, games, myths, anime etc. In Fire Emblem, there's always a sword with the sole purpose to defeat dragons with a description like "embroidered with ancient magic/ sword from the gods to slay dragons." Fairy Tail, an anime created in Japan, are about Dragons only being able to be defeated using Dragon Slaying Magic, which many of the members in Fairy Tail possess. In Pokemon, Dragon is weak to Dragon, Ice, and Fairy. If we are basing these type advantages/disadvantages on other examples of Fairy and Dragons, it only fits perfectly.
Um no. Dragons were equally immune to enchanted weapons as they were to direct magical assaults. A weapon that can harm Dragons usually was anti-magical and could cut through the magic that defends them.. As for Fairytail, why is Dragon Slaying Magic the only magic that can harm Dragons if they are supposed to be weak to magic? And no "Many" is a wrong word. There are only 7 known Mages with Dragon Slayer magic, 4 are in a guild of roughly 100 people. That in no way is many.
Divine weapons also are not magic. A Weapon from god has no magic in it, its a divine weapon that nullifies magic since Magic is a manipulation of ones will upon the planet and no one's will is stronger than that of a god. No magical weapons in stories were ever used and made directly for killing dragons. None of them have ever said, poke it with this and it'll die.
Some that I know of were enhancements to increase the weapon's ability, such as making it sharper than humanly possible, this would allow a sword to cut through the thick hide of a dragon. A Sword that would erupt into flames wouldn't do anything to a Dragon.
And again there are no stories that exist where the Fairy is not a sniveling coward when they meet with Dragons, so no there is no sense in Fairy being stronger than Dragon.
Also, if Dragons are immune to magic, then what is Ice? Why is Ice strong against Dragon? Because it freezes them? If you say Ice has nothing to do with magic and such, then we can say the same thing about Fairy. Why? Because in the Pokemon World, Ice, Dragons and Fairies are whatever GameFreak wants them to be. GameFreak has told us that in the Pokemon World, Fairies are strong against Dragons. We can't argue this is stupid or makes no sense because it just is. It'd be like saying that trees giving out oxygen and taking in CO2 makes no sense. Just accept it, because I'm 99.99999% sure that GameFreak aren't going to change this because of a few close-minded haters/fans.
Ice has nothing to do with magic. Its not magic. Its a natural element. Magic would only be classified by unnatural occurrences. Magic is a will that can mold the elements into use. As for why Dragons are weak to Ice in Pokemon, this is because of real world allusions. Dragons have no real world animal to directly relate to. So they are related to reptiles since they all look reptilian for the most part. Since Reptiles die when put into cold environments, Dragons were given weakness to Ice. Dragons in Pokemon are cold blooded or believed to be such since they are related to reptiles and cannot produce their own heat so cold temperatures are deadly to them.
Do you think maybe they'lll change existing moves to fairy-type? Like how Bite and Gust went from normal to Dark and Flying, respectively? I'm thinking moves like Moonlight, Wish, maybe even Flash if they agree to let dubbers decide to call it Light (which they may want to do).
A lot of people believe we'll have some, especially a few you named, changed to Fairy Type. Personally I don't see anything changing type.