I sent Tom a deposit on one years ago -- and trust the Rbros to come up w. a good one. Personally, I agree w. Tom -- about a 1/3 increase in size over the R9, single stack, maybe w. a gutter sight, and either a heel release, or a trigger guard release, similar to the Walther PPS.
In the world of fantasy, it'd be able to take 1911 mags, but I really doubt it's possible.
Now, in my wildest dreams, it would be a P7 in 45... but, then it wouldn't be a Rohrbaugh, it'd be a P7 in 45...
Personally, there's a world of more "combat" or IDPA oriented pistols -- I like the concept described above as being an ideal carry gun, even if you do give up some reload speed, for not being able to bump the mag release.
I think the trigger guard release is a good idea -- almost as reliable as a European style release, and not much slower than a push-button -- I think a button release in the heel, same as the P7 PSP, is also a good idea.