The problem I have with the product is that they are essentially replacing the GPU obsolescence schedule with the chipset obsolescence schedule. And their platform choice makes this particularly bad because while AMD makes an effort to keep their sockets backward-compatible, Intel seems to do the opposite. In fact, Intel now seems hell-bent on segmenting the platform space as much as possible while constraining the product lifecycle as much as possible. Want to reuse your C2Q or upgrade to a 6-core (gulftown, is it?) CPU on this mobo? Good luck with that. With socket 1156, Intel has effectively forced you to buy a new mid-range CPU and constrained you to the mid-range market. If past behavior is any predictor of future behavior, I fully expect the next major generation of Intel CPUs (e.g. 3+ yrs out) not to be compatible with 1156. How long do you think Intel will make advancements on 1156-compatible CPUs?
So, yes, you can mix GPUs from different generations and even from different vendors. But by the time it even makes sense to do that twice, you'll need to upgrade your whole MB to keep a balanced CPU-GPU system. If the X-mode, A-mode and N-mode scaling were more seamless and effective on the latest HW, and the cost were more in-line with other 1156-socket MBs, I could see this MB making some sense. But given that you need to spend an extra $150+ for this Mobo, I'd rather put that $150 towards the second card or an upgraded card with a longer life span before obsolescence.