I did a video about it just yesterday - And to summarize what my theory is about:
First off we can take a look at the names which most likely will be for the two mascots, if in fact these trademarks are for Pokémon and not something entirely different.
Solgaleo and Lunaala have a very spanish vibe to them - even though you could say that about many languages.
But what else is there to consider? We were just in Kalos, and we stumbled upon a very strange Pokémon, that being Zygarde. Of said Pokémon, we have seen in game art, same goes for Volcanion which we in the west did not receive, which points toward us having to wait for later.
Now we also know there is a railroad track in Kalos that goes somewhere, but where exactly could that be? I personally think that there are too many signs pointing toward Spain to ignore it.
We also clearly heard that we haven't explored the souther half of Kalos, and what lies south of Kalos/France? Spain.
Now when it comes to the Pokémon themselves - Solgaleo is very likely a Lion, that'd make perfect sense. And I'm not mocking you, by no means, you guys who say GameFreak are more creative than using "Solgaleo" for a lion - But I mean, Politoad? Hunchkrow? They haven't been that creative with 90% of their names.
So it being a Lion just seems right. To continue on, we received Litleo/Pyroar in X and Y, which could be found in the mountainous area in southern Kalos - So couldn't it be plausible for there to be a connection between Pyroar and Solgaleo?
For Lunaala, I must admit, I did not figure out that Ala means wing, but to be fair, I didn't think, and I still don't hope, that they'd make another legendary bird right after Yveltal.
What I though of, was a Wolf, possibly with wings I guess, who'd be accompanied by something like Zoroark, Mightyena or Absol, just to pick a few canine Pokémon.
I think it'd be cool for there to be a sort of following around these Pokémon, which is my reasoning behind linking older Pokémon to the two legendaries.
This is a very short version of my theory - But what do you guys think?