That would be a step beyond major. It wouldn't warrant a mere press release announcing an announcement, it would require fliers be dropped across every major US city announcing an announcement taking place atop the ugly Sony building in Manhattan. Of course, MS' biggest flaw (Especially when compared with their old rivals Apple, Netscape, Google) is that they lack style, so maybe they would do something silly like merely shake hands with their new subsidiary at a public conference.
They laid off the entire Game For Windows Live team.
I have a feeling that they did that the day after it was announced.
I'm going to be a doubter and come down on the side of "Who cares?" I have a feeling that whatever they consider "major" isn't something I'm going to care about as a gamer because if they had some huge game related announcement the time to roll it out would have been during their E3 press conference so that they didn't come off like the schlubs that they did.
__________________ I'm bad, and that's good. I will never be good, and that's not bad. There's no one I'd rather be than me.
I'm sure this will end up being not such a major announcement.
Having said that, it would be brilliant to dupe Sony into not showing their next console at E3 only to show their own only a few weeks later with nothing to divert attention away from them - particularly if they're shooting for a Spring 2013 release.
If a tablet, I think it should have some connection to current Xbox 360 platform to make it instantly interesting/worth our time. I doubt a DVD drive (making it a true Xbox SKU in addition to its tablet features), perhaps it will allow us to access/play our XBLA/Games on Demand library, or cache (install) some number of games on it (not sure how we would get our games on the device). This is doubtful I suppose, as there's not a lot of money to be made in giving us new ways to play what we already paid for. It would make it appealing on day one for a lot of people though. You could put the thing in a stand and play games with existing wireless controllers. I am going to be the loon and say that I would love a tablet with slim DVD drive on the back, despite the size it would take up, if I could run all of my Xbox titles on it.