I like the idea. Though, I would think you shouldn't be able to earn talent points as, say MNK, then be able to reinvest them into the NIN spec, without ever touching NIN. If this were to be considered, I'd like to see that you'd actually have to "level" each spec to earn its own respective talent points, or to unlock tiers that you can invest in. Otherwise, from a character-development standpoint, it doesn't make sense that you could be a master at something you've never trained for.