There is literally, LITERALLY, nothing stopping you from playing rogue past 30 beyond the community preconception that classes are worthless and should be abandon for Jobs the second you hit level 30. For the stat boost you lose from not equipping a Job you have near boundless multi-class potential. If you want to keep playing rogue into 50 I say go ahead. Most if not all non-AF/Relic gear is for classes and Jobs anyway so you will still be able to keep adequately geared and with the new high level crafted gear you can even use materia to make up for the loss from not equipping a Job. Wanting a Thief Job is really just want to have your cake and eat it too. I mean, really, a DD class with two DD Jobs... not going to happen.