If they wish to give Gyarados another mega-evolution in future--I believe it might be possibly, as they give extra mega-forms to Pokémon depending on popularity (Gyarados is rather top-notch in regards to that--it'd be sweet if it were partially dragon.
This Pokémon's story would be sort of similar to the one of Charizard; many of us fans had wished to see it become dragon-type someday, and they had finally done it with giving it a secondary mega-evolution form. Though, only thing I have disliked is the major color change, which, if you ask me, is out-of-place; if it weren't for that, I would have loved it. I hope they don't do the same with Gyarados, if they're planning anything.
It's got access to a few dragon-type moves, I believe, so if it does wind up gaining a dragon-type mega later throughout, it could likely take some decent advantage of them, which is great!