i'm not sure a separate blow up pfd in a bum bag is going to cut the mustard with race officials.
the bum bag with the attached pfd with a gas canister barely gets you to a race start with some refusing them.
personally i can see everyone eventually 'wearing' pfd's although heat stress becomes a issue in some 'hot climate' states.
most know my story a few months ago now. i passed out in the water was one part of it. no warning, no i'll just lie on my board or something. so it makes my think a full supported pfd would be safer.
if you fall and get knocked out or just pass out a pfd bum bag isn't worth jack sh1t in reality. and lets face it- even in non race dw ers most times you wouldn't know what the guys behind you were doing if everybody is experienced and no ones worried about novices
the old saying- prepare for the worse and hope for the best goes out the window for comfort when it comes to sup paddlers