Re the Silver mascot thing, I'm inclined to think it's not so much coincidence. Crystal has been the exception thus far which doesn't mean that much (patterns get broken, only two other 'third games' as well), but I feel it's quite possible that Crystal hadn't been originally planned when GS were made too (and there is the claim that GS were intended as the final games as well which fits that). I'll also agree with the event-Pokemon-not-being-it thoughts. They're basically event Pokemon to be given in wifi events or link in with shop promotions (toys r us, eb games/gamestop, etc), the latter which nets them free advertising for their games, as well as give customers small things every so often to keep them interested in the games after they bought them. It's be weird for them to remove one of those now for the third version.
So hence I'm going with Kyurem being the near-certain mascot for a third game if it happens, personally.
I'll also note that iirc there is data for Kyurem to know extra moves that it cannot currently learn in BW in
Freeze Shock and
Ice Burn (notice the names and effects and think about Zekrom and Reshiram's typing). In fact, those two moves are currently not learn-able by anything. New moves cannot be easily added to games within the same generation because that can cause compatibility issues (for trading/battles, and why for instance TMs remained the same between 3rd and 4th gen games... and although they changed in 5th gen, guess what's not transferable between 4th gen and 5th gen? That's right, any items including TMs). Interesting data for BW to already have in place then, no?
As for the name of the game if it happens? Not placing my bet on anything. Why? I need to look no further than the fanname for Platinum (in Opal) being so strongly believed in that when the name Platinum was revealed a lot of people firmly believed it must be fake. So much for that!