I think I'd prefer a mix of role and cross-class, with the proviso that everyone gets vital kit built in (provoke, diversion, swiftcast, etc.) Have classes get a key skill at 15 and 30 that goes into a role pool and have jobs pull from two role pools.
It'd have to be part of a proper rework of the leveling process though. I think classes should have more abilities earlier on, we'd also probably need a class for Scholar, to keep the amount of classes in each role even.
I'd end classes at 30 too, want more skills, get a job.
So with that in mind, an idea of possible level 15 and level 30 unlockable skills:
Tank role:
Gladiator - Awareness, Tempered Will
Marauder - Convalescence, Anticipation
Healer role:
Conjurer - Lucid Dreaming, Largesse
Librarian - Surecast, Eye for an Eye
Melee DPS role:
Pugilist - Internal Release, Invigorate
Lancer - Second Wind, Bloodbath
Support DPS role:
Rogue - Goad, Feint
Archer - Palisade, Peloton
Caster DPS role:
Thaumaturge - Manaward, Mana Shift
Arcanist - Addle, Apocatastasis
Then, yeah, jobs pulling from two sets. Make it so you have 4 slots, gives you 8 skills to select per job. Anything you want can be achieved by level 30, but I tried to keep them from being proper job killers to miss.
I don't know, I might be trying to make a broken system that most people hated work, I liked it though. I thought it was cool when I first started so I might have a bit of nostalgia for it.
In a game where you can level everything on one character, the idea that leveling extra classes grants you extra skills just makes sense to me.