For the average flyer, how much real estate do you really need? Computer, switch, and battery? Sometimes double that, and really, how often are you really doing dual redundant dual deploy where you invest in 2 sets of computers and batteries for 1 rocket? If you are, chances are that it's because the rocket is either unique or expensive enough to warrant it, and you go into the project knowing the technical hurdles.
The only issue that I have with conventional av bays is that if you put the sled on the all thread is that you lose SO MUCH space in smaller bays. 4" and greater it's not much of an issue, but get into 2.56 and smaller tubes and it takes some serious planning to get 2 computers in there, or one computer on the conventional stand offs. Pain in the butt.
I find it much easier to just cut a piece of ply that's the full diameter and full length of bay. The bulkheads will keep it from moving, and I've not had to worry about it spinning at all..