They're probably also not against the idea of the England contingent all playing for just 3 or 4 clubs do that the players are used to playing with each other.
For the last xx years, it has pretty much been this anyway. With a normal distribution, one could expect 80% of the England players to come from 20% of the clubs.
Do the stats back that up? Sarries, Quins, Tigers and Bath I would guess make up the 80% (yes, I know, 4 clubs is 30% of 13). The reality is, four clubs is about right and all that would be needed to meet your RFU requirement to make the England squad, leaving 21 clubs to be in the Championship, and feed to those four clubs. Lose a club somewhere along the way and have two geographic leagues in the Championship, with no promotion or relegation from the Premiership. Trouble is, if you really want fans at the Premiership games, those clubs do not have the best/biggest grounds. Not that I think concentrating the Premiership would cause fans to switch cubs anyway, just to watch Premiership action.
And that is the point isn't it? The RFU see rugby fans as homogenous, willing to support and go to whichever club the RFU tell them to.