The idea of pro clubs spending even more money to get players, when they can't afford what they've got now, is probably not going to fly.
There are a very small number of clubs (4 perhaps) who are being squeezed here. you could argue that the other CC clubs have accepted the situation and are rolling with the punches that Sheffield, Fax and Fev are taking on the chin. I look at the bottom of the SL and I see 3 or 4 clubs who are no better than these. Realistically there are 3 bands - the clubs that can sustain fully-pro, teh ones who think they can and the ones who never will.
The gap betwen the Championship and last year's U23 league is massive. 90% of the players who turned out for Sheffield last year would have had better quality, more regular, rugby by playing in the NCL. The bottom line, and I'll bang on about this again, is that we just don't have enough players, full stop.
It needs those clubs who genuinely want to be SL clubs and all that goes with that being in SL and those that don't surviving as best they can.
I am not sure the figure is 4. Certainly Fev and Sheffield want to be SL clubs that develop players. As you say in summary the game needs more players.
But in any case a 16 club SL with a smaller salary cap may well sort this out, as may the demise of a couple of SL clubs who may not be able to hack it even at a lower salary cap.
Get the 3 bands you speak of down to two.
Get more pro clubs who can stimulate more kids to play and adults to help.