Won't work in the WoW-like model FFXIV is pursuing.

It will be difficult for latecomers to "catch up" - unlike with gear which you can just buy of a vendor after a bit of grinding.

I can see the appeal of getting more (optional) abilities but that is a no-go as well as it will mess up raid balance - in addition to making it harder to for latecomers to raid.

Basically anything that has to come into "contact" with raiding is "constrained". There are many things you cannot do.