I'd say to everyone wait for the announcements more than anything else, I mean for crying out loud we're only a matter of a week from E3 now.
The major thing to remember when dealing with Microsoft announcements is that primarily everyone will always jump to certain conclusions based on rumours, or if technology is similar to another companies (i.e. Reals and Miis) instantly people pick apart the differences even before release.
I've said it before about the Reals but the way Microsoft have integrated them is different to how Nintendo has and Sony are planning to introduce their Avatar system. While they might not have become such a major component as many felt they would do, honestly that wasn't a bad thing. Personally I've found them great to just look at a party and be like "ah such'n'such is in there", without having to go via the guide blades to look at the actual names to just take a guess based on the umpteenth person to have a gamerpic that is either Marcus or Masterchief...
As for motion controls though, while it's a nice rumour this rumour has been around since Nintendo and Sony showcased their new control systems. Although it might not be exactly commonly known, Microsoft have been experimenting with a number of control systems for a very very long time; hell if they hadn't Microsoft Surface would never have appeared.
A number of the MGS companies have also been playing with similar "depth touch" control systems using the Live Vision Camera, in-fact most of what they did helped come up with a fairly awesome API within the XDK for using the Live Vision Camera as a controller which I think has been unfortunately ignored by almost every developer.
Personally I reckon if anything this job posting probably has something to do with them getting a bit more exposure for that control aspect, no doubt working on things primarily for Xbox Live Arcade. Then you've also go Voice Control, experimented with recently by Ubisoft something that might be useful for some stuff you want on primetime. It also could mean they want to have a few games for those with disabilities, like some of those games for the deaf that utilise sound in some crazy way that allows you to play without intense graphics.
Then again it could be something more mundane as perhaps focus on Artificial Intelligence that makes you feel more like you're playing with a real characters rather than lame NPCs, this again could be a likely candidate given the push in the last year for better AI plus the fact that the Dream-Build-Play competition was heavily focused on that aspect of the games and that the winners would get invited to work for MGS.
There are just so many possibilities that thinking of only Motion Controls as "the" only possible "innovation" being quite constricting. Especially as I've yet to use any motion control system that doesn't make you feel more detached from the game rather than more so... just because it's possible to add something doesn't mean it works well enough for gaming needs. Especially as motion control in the same way Nintendo or alike employ it really appeals to the Casual market far more than the Gaming market that Microsoft currently holds; with Nintendo already keeping a firm grasp on the casuals I don't see Microsoft being stupid enough to try to grab them at the expense of their consumer basis that is currently providing them a huge income from their digital business.