I did see that on the internet about them all being locked in for nine years. That would seem to indicate at least two more movies.
I remeber Brent Spiner having a multi-movie deal with Paramount as well. However, it wasn't limited to Trek. He was signed for a certain amount of movies, but they didn't have to be Trek. I want to say that this was after Generations, while they were getting ready for First Contatc. Spiner did appear in that movie (obviously) along with appearing in "Phenomenon" with Travolta. I think he may have appeared in something else as well.
My point being: Even though they may have signed a three picture deal, it doesn't mean that all three have to be Star Trek. The deal is with the studios, not the franchise.