I think the game can be designed in a way that jobs can move away from the trinity without having to entirely do away with it altogether. As the previous poster said, Paladin is a good example of a job that, whilst not being limited to only tanking (it can heal, it can support the party defensively) still fits very well into the mold of a tank. Naturally there's problems with its design as well, but this more related to content design than the bigger picture of the 'trinity'. Technically you could argue that every dps (bar Monk, Black Mage and maybe Dragoon) is a support/dps hybrid anyway, since they all have equal amounts of utility.