I don't think the devs would keep having new jobs start at level 1. If jobs are going to be gated behind expansion packs like Heavensward did, then people are going to get tired of having to go back to very old areas just to level up their new jobs (or new low level areas if they even do that) before they can even begin to use them in the new zones and dungeons. I don't want to have it where 75 is the next cap and I have to start at level 1 and play the same old content for the umpteenth time for a new job.