Its something that Premier Rugby wanted in order to bargain their way with England - dont think it'll ever happen though.
Looking at what Bristol have achieved in only their second (?) year back in the premiership, they have no argument whatsoever for that, since they've disrupted to constant yo-yo system...
They'd, In my opinion, be better off moving 2 teams across, then they'd get a greater competitiveness between premiership and first division clubs, and then having some competition comparable to the FA cup, although have the premiership clubs pooled in in the fifth round of something similar, so that it isn't a massive burden on their timetabling...