The problem with leveling alt jobs, imo, is that for groups, there is always one "efficient" way of doing it, and everyone flocks to that. It doesn't matter how many options SE provides, only one will be used. Like, I actually like FATEs. I find them relaxing and I like wandering around the open world. But ever since Palace of the Dead came out, no one does FATEs at all. If SE comes out with a new system to level that's more efficient than PotD, then PotD will die.
They can make multiple solo options for leveling. But I don't think they can make more than one (maybe 2 at most) group options.