I really don't even see the point of adding a new class/job in general. We basically have enough jobs to fill all the major roles needed, with the way the game is designed adding a new tank or healer won't add much. We basically have all the healing we need, this is why astro seems so lackluster. As far as tanks go the 3 we have cover everything that would be needed and anymore would be overkill at this point.

Adding another DPS job doesn't make much sense either seeing as we have basically all forms a DPS job can really take in game already, between DoTs, burst damage, ect. Anything new at this point is just going to seem lackluster, there isn't a niche that another job can fill to really add something to the game. This is why hybrids, like what astro was trying to be(High risk rng buffer with some heals)didn't work out and ended up as a clone of whm.