I personally expect more than just raw performance from the next xbox, though. Besides the obvious advantage of developer tools from MS, I'd expect the next xboxs hardware to be flexible in order to prolong its life and detach it from the usual software upgrades.
Honestly I'm more interested in how the next xbox will tie in with Microsoft phone, tablet and pc. We know that the next xbox will have great tools and developer support already, and spec wise we're getting dangerously close to the point where hardware spec is mattering less and less in the grand scheme of things. I mean lets face it, a far better graphics alternative, the pc, already exists an no one cares about it. That's because what matters more now is the software experience, not graphics. People will ultimately live and play on the box they have even if it looks dated. Hence why for the next Xbox I'm far more interested in the software tech than the hardware tech. Microsoft nailed that with XBLive which is brilliant, but right now that's locked onto just the one device, the 360, which limits its grand scale appeal. I'm curious as heck to know how they bring XBLive to every device and tie them all together, I think that is where the money shot is. In an ideal world pc, tablet, phone and console all look and run similarly and all run XBLive, and all have cloud support from the get go. One XBLive account, one cloud, one set of money, one set of media, one experience across all devices along with some interoperability. Sharing music and movies across all devices is the obvious one, but i'd like them to go beyond the obvious. Aside from Apple I'd say Microsoft are the only people in the position to tie together the four main devices in use today (computer, tablet, phone, console) so it's their's to lose.
I'm guessing at the bare minimum we'd have to wait at least 6 months after Win8 and Windows tablets come out before we see another Xbox console. I figure they will want to get Win8 and their tablet out and iron out any issues with the new interface, and then transplant that experience to their next console, all of it being touch/kinect aware out of the box. I think that makes 2012 impossible for a new Xbox, but 2013 might be doable unless their year over year sales keep going up in which case no chance.