Microsoft has put out a press release about the "bringing it home" event they are doing for TGS & X06. Included in the press release (available here) was the very interesting quote of:

While there has been tonnes of speculation around the net this morning as to what this is, it's interesting to look at the wording. First it looks like this will be the actual release of the game (otherwise this will be the first time that we've seen a preview video on Live for a XBLA title). Secondly it's a "never before announced" title, which rules out Dig Dug (it was announced at E3 this year). What this leads to is the theory that this game will actually be released on the 27th, the first day of X06.

What the title is, is anyone's guess, but considering all the Virtual Console info that came out last week, I'm betting that nobody will be denying the fact that this will be a "major" release.