Although this seems like the chances of Sonic being in Brawl is greater, it is actually less and here are the 2 main reasons why:
1. The game is set to be released around Christmas. That means that unless Brawl is release in 2008, then all the hype the Mario vs Sonic idea would get would be transferred to Brawl and no one would buy the Olympics game. It's like why would you buy a sports game where they race and throw discus when you can buy a game and they will beat the sh*t out of each other.
2. Legality. Now that the Sonic vs Mario idea is tied to the Oympics, the Olympic committee would be stupid to allow that idea to be transfer to other games within a certain timeframe. Like they would have the right to withhold licensing of the Olympic logos, titles, and whatnot from SEGA if another Mario vs Sonic type game was announced to be released within 6 months (more likely a year) prior to or after the release of the Mario vs Sonic Olympics Game.
So unless Brawl gets pushed to Summer of 2008, then Sonic will not be in Brawl so stop asking. Although if there is some kind of downloadable content then he may be released later on (IE he is programmed in along with several super hidden characters, but in order to earn them you must d/l a code from Nintendo to unlock them, but even that's doubtful)
Besides, having Sonic in the game would totally overshadow having Snake in the game, making Konami feel like it was a waste to give Nintendo the rights to add him in,
1. You'd have a fighting game for those who like fighting games, and a Sonic party versus Mario party game, where it has not only Sonic, but Knuckles, Tails, Eggman, Shadow possibly, etc. It would just show that Sonic and Mario will star in more games together.
2. Not exactly. The IOC doesn't necessarily lose anything from having Sonic star in other games after this one. Also, Super Smash Bros. Brawl isn't a "Mario vs. Sonic" game, it's a pitting of every Nintendo all-star. That would be like saying that Snake cannot star in any other games now because he's confirmed for Smash Bros. This game, after one drop of information leaked on the first day, gained amazing publicity. Just because Smash Bros. releases around the same time as this game, doesn't mean people won't buy this game. I'm not buying this new game because it's "Ohhh, Sonic vs. Mario!", but because it's a new party game, new games, and this time it's Sonic and his friends against Mario with his.
Not unless Sonic is already in the roster. Sega and Nintendo decided not to leak any information about Sonic being in, but with Brawl being in the works, and this game just suddenly appearing pitting Brawl's most wanted character with Mario, it makes you wonder if he's already in, in which case, what would the IOC do then?
And Snake being in is because Hideo begged Sakurai to include Snake. Snake's new game, MGS4, is appearing on the PS3, hence the publicity thing doesn't work as well putting him into a Nintendo game, does it? If someone bought a Wii, and Smash Bros Brawl, because they wanted to play with Snake, then the publicity worked in Nintendo's favor mostly. Nonetheless, Snake's in the game, he's already confirmed, and he's already being recognized before the game even releases. It's not about being overshadowed, we know he's there, we know who he is.
Because with this Olympics game, Metroid and Galaxy already on the 2007 release list, Brawl cant be released this year without cannibalizing one of those three major games...
Sakurai and Sora have nothing to do with the new Olympics game, Metroid or Mario Galaxy, the game could just as easily release this year.
