I think the biggest limitation that would need to be overcome for a mixed det of 2 is dealing with expectations. Yes, administratively you can have the same aircrews fly both aircraft (see my repeated posts on going back to a HS concept). But the Mx on a small boy is unique, ESPECIALLY if you're doing SAG/independent ops. While you have two aircraft, it's really 2 to make 1. I forget what the PAA is, but I don't think it's much more than 1.1-ish.
You typically don't want to fly both birds evenly in order to keep the phases spread apart (an even bigger issue for a D-phase) as well as managing FLM (or whatever it's called now). So there's some balancing that occurs between Mx and Ops. Invariably there are parts issues, which causes one bird to be hard down for the duration of that steaming period (but maybe not always the same bird, day to day, if you can CANN a part).
There's also the issue of managing expectations with the ship's CO (and OpsO). I've done 2-plane dets where both aircraft were evenly matched (2 FLIRS, although cabin configuration would be different so we had one ASW bird) and that's easier, but I've also done deployments where one aircraft was more equipped than the other (relatively speaking), so the ship would always want to fly the more capable aircraft, which wasn't realistic. Obviously it would depend on the mission and CO's mindset to determine which aircraft (S or R) would be more valuable, but that CO would need to understand you can't use just one exclusively.
It's all doable, no doubt. Given the relative amount of shooting that's been done historically, and the limited amount of LOG that's actually done during independent ops, personally it doesn't make much sense to me to give up the radar (and possibly ESM or ALFS, depending on the mission) for what basically boils down to a little more room in the back, but with less fuel. But I can understand the argument.