Half measure f2p doesn't work too well when you crate two classes of players: the haves and have nots. Esp. with the state of current f2p offering extremely high quality and full access.
One of the best reviews I ever seen of Rift was; "It's eh. Good game but I wouldn't pay or it."
That probably sums it the game for the majority of players that have played at one point or would consider playing. They certainly aren't gonna pay for xpac when the first half is obsolete. Free though it may be.