Since SE loves to abuse nostalgia so much, they should at least do it right.
Final Fantasy 9 Passive Skill System is the perfect system for Cross Class Skills in FFXIV.
You have a certain amount of SP (based on Level), and each Skill requires X SP to allocate, allowing SE to tune each Skill perfectly.
It is infinitely better than having a static amount of skill slots and trying (and failing) to give all skills an equal value.
Plus, I think it would be nice if there were Cross Class Traits as well.
Combined with Cross Class Skills, it could enable different roles or simply different combat styles for the same Role.
FFXIV is lacking a lot in fun/variety-oriented customizability within each Job.