The main thing holding back DSLRs is the moiré, and no other feature will improve the IQ unless they address this issue. Canon claims to have fixed it in the 5DIII, but since they haven't been releasing very much footage (or highly compressed footage), and knowing their track record, something tells me it's BS.
The hype over 1080p60 is just people on the internet gawking at numbers, as per usual. 90% of DSLR users are outputting to web, and if you think there is a visible difference between 720p and 1080p DSLR footage displayed on the web, you're delusional. Bearing in mind Canon's line-skipping compression, the difference between 720p and 1080p is the difference between whether it skips 1 or 2 lines at a time; it's trivial. The in terms of actual detail, 1080p has no advantages over 720p. The main difference is that 1080p has less moiré due to it using less line skipping (though moiré is still an issue), and it's bigger. That's it.
So basically, adding 1080p60 will give you the same image in a larger frame. To think this is somehow an improvement is to say that bigger is better with complete disregard to quality.  I'd rather shoot 720p with a solid codec over 1080p with a shit codec. Fix the compression, and you have a completely new camera.
If you want to mix 720p with 1080p, scale the 720p up to 1080p during transcoding. It looks exactly the same.