Shawn Asmore, who played Iceman in the X-Men films, has said that he's heard the rumours about an X-Men 4 film, but he was told that X-Men 3: The Last Stand (review) was just that, the last stand.

According to Coming Soon he said:

"I know they are doing a Wolverine prequel and I've heard a rumor about a Magneto film... those are all in the past like prequels and origin stories, so I don't know. There are rumors about an 'X-Men 4,' but as far as I've been told 'X3' was going to be the last big ensemble 'X-Men' movie. I would love if they made another one, but I'm not sure that they will,"

Nope, and I agree with you, as I always have. I think that's the last we'll see of the big ensemble X-Men. We might get lucky and maybe see something that's got a completely new cast of characters, but there's no way it's financially viable to get all those stars round the table and renegotiate their contracts for a fourth film.

Sure Ashmore has a contract for a fourth, that'll be the standard retainer "in case of a sequel" clause, but that's only because he's one of the newer characters and is much cheaper. I think you'll find that missing from the big names.

Anyway, I'm pretty sure they've identified the market is in the spin off, not the ensemble.