On current form and over the past couple of seasons, you'd have to say it can't be many. How many players have we had in the Championship team of the year in recent years? In 2007 we had stand out players like Ollie Wilks, Damian Blanch, Scott Grix. They stood out in this division and have proved since then that they could make the step up. With having so few stand out players now, I don't think you can make a solid claim that many could make the step up. Even experienced players like Finnigan haven't stood out IMO and no reason (at the moment) to think the club would be looking to him to play and do well in SL.
My list would be very much open to change depening on how players go over the next few months, but here's what I'd go with at the mo:
Paddy
Heckenburg
Craven
Plus the most of youngsters like Mullally, Kelly, Lunt, Scott etc.
As a seperate point, I'd get rid of I'Anson, Pickersgill and Ropati tomorrow if we could, with Leuluai on his last chance. Some of the players performances over the past couple of weeks have been so bad, they should count themselves very lucky if they given any game over the coming weeks. As suggested already, the fact we have got the nod now, there's no reason why Betts can't give more chances to the youngsters. IMO there's no point wasting the rest of the season playing players who are not going to get given a SL contract.