To go out on a limb, I would say that the presence of Manly, Roosters, Souths and STI would seem fairly certain, provided that Manly can secure their off-field future. Brookevale, IMHO, needs to be upgraded to a boutique modern stadium. When it rains there, crowds often stay away in droves. Although everybody is attached to the idea of the hill, I think non-seated areas such as those at some English stadia (Warrington's home ground, I think, for example?) might be the way to go. Of course, all of this takes money.
Looking out the other way, Wests (well, they're half out there) are looking good as are the Bulldogs. Parramatta need to get their act together and Penrith really seems to die off with a lack of onfield success, arguably more than other teams.
This isn't meant to be my idea of which teams should stay or go necessarily. As I said yesterday, that is for the NRL to decide and their analysis should be a great deal more rigourous than mine on a forum. My gut feeling, though, is that six teams might be a good number.