I have a feeling the class system is on its way out the door, just going by the fact that the Heavensward jobs have no class requirements (30 THM/15 ARC for BLM) to unlock like the original jobs do. As for cross class skills, even that system is kind of a mess. We got Goad as a cross class skill when Rogue/Ninja was introduced but no other job can use it with the way the current system is set up.