I feel if they don't add more all around skills to the base classes. Defensive, Support and Damage type skills i expect at some point our Class traits to actually be replaced by a job stone. It would likely be one of the easier routes for them to go to start.

Then the remaining issue is how would a Dark Knight use Aegis boon. Job stones "re-names" and "re-icons" the skill to have the same effect, but to use a Greatsword block. Shield Bash becomes Pommel Bash etc

You may be used to the effects, and thus it would provide a smoothish transition, since i don't expect them to want to Totally change the experience from class to job to job except in a few cases (Summoner)

This wouldn't be my personal favorite solution, i kinda want each class to be able to do all three to differing levels of effectiveness, and the Jobs they recieve specialize them. DRG is DD, maybe some new Job they use a Staff like Spear as a more defencive Parry tank etc.

But my personal favorite basiclly means adding to each class alot more skills (and depending on your take on long lists of skills, you may like or dislike that. Which then means more cross-class options, which likely means balancing, which usually leads to skills that feel like they do nothing much, because if you cross-class a bunch of defence skills you'd be too hard to hit unless they make the cross classable skills a very tiny list...which kind of hurts the class idea a little, as much as i like it.

Something tells me my last paragraph is one of the things thats giving SE some headaches right now over how and where to take classes themselves.

Thats why my expectation is Traits swapping out, if its well recived by the community, they may just say, "They seem to like it enough, so we don't have to delve into the tougher idea." As much as i wish they would.

Making Job exclusive traits could also free them up to make the class traits more interesting for the classes themselves. Perhaps giving them their own interesting twist. Lancer with more parry due to trait? Parry materia looks slightly more interesting for a Lancer maybe? GLD defencive traits swapped out to Offencive traits for Dark Knights? Then DRK from GLD looks much easier to impliment.

Now going from 1h to 2h sword via armory system. Thats a different can of worms.