Okay starting off.. I first started this game during the beta of 1.0, and yes the game was a mess back then. One thing it did to that was sort of interesting though was that it allowed you to take pretty much any skill from any class and mix them together to pretty much make your own class. I very much enjoyed playing as a gladiator and equipping spells and heals, it was pretty fun just customizing my class, even if the game was clunky.
As of now, at level 60 you are the same as anyone else of your level. It's really boring to be honest... I think there needs to be some sort of customization allowed. Honestly, what's the point of the cross class system? They lock you into 2 jobs which only have a couple of skills that are actually useful. Just like the stat point system(only tanks can really choose), why even bother having it?
Now FFXI wasn't perfect, in fact, it did was a mess most of the time... But one thing that I always appreciated was the sub job system. Even if there was pretty much a perfect combination for every job, it was still fun to do stupid things like BLU/DRG or get some good laughs out of the guy who is running around as WAR/WHM.
I think FFXIV should allow you to choose your two supporting jobs, and also open up more skills to use in cross class so that different combinations would be competitive(also, open up damage spells on melee/melee attacks on casters). It may cause some unbalance at first, and people would use certain subs for the most part only, but even still, the option should be there. Many people actually enjoy customizing abilities, and developing their own style.
Example of what should be allowed on THM sub:
Fire(would be interesting to get astral fire/umbral ice @ 1 stack on other jobs)
Fire II
Blizzard
Sleep
Lethargy
Aetherial Manipulation(This could be nice on some melee jobs)
Example of what should be allowed on ACN sub:
Bio
Aetherflow(1 Stack max, would love to have this on DRK)
Energy Drain
Bane
Example of what should be allowed on PUG sub:
Boot Shine
Twin Snakes
Fists of Wind
Perfect Balance
Arm of the Destroyer
Example of what should be allowed on LNC sub:
Heavy Thrust(would probably be a bit broke as a cross class, but could be adjusted)
Life Surge
Leg Sweep
Ring of Thorns
Of course this would throw the current job balance all around, but the skills could be slightly adjusted if they proved to be too broken when subbed. Allowing customization like this would definitely make the game more interesting. Just think about going DRK with ACN/GLD subs, you could use bio/bane Aetherflow, and still have provoke to tank swap/grab aggro. Or you could go LNC sub on GLD to take ring of thorns for some AoE damage that PLD lacks.
I know, something like this will probably never happen. But even still, I think the direction they are going with the jobs is a bit stale, and could really use some more thought to it... Any kind of additional customization at this point would be welcomed.