I was sort of against it but I've been thinking about it and it would be handy in some applications. I wouldn't mind having one for my MS. I bet it would increase accuracy a bit. I'm building mine in 6mm ar (6.5 grendal necked down). It would be like a small frame rpr but better. Put an adjustable gas block on it. Close it off when you swap out the bcg and you have bolt gun accuracy.
Plenty of semi auto's out there that can shoot half MOA. The reason most don't shoot well is the quality of the barrel. Most factory barrels are crap. I used to have an ATRS stainless match grade barrel in one of my AR's that would easily shoot sub MOA. I wouldn't be looking at a bolt action upper for an AR for increased accuracy, if you want one go for it but I'd like to keep that option on the back burner until the stupid Libs ban semi's.