Some systems in FFXI felt really intuitive, and I would happily welcome them in FFXIV. Of course, everyone is open to their own opinion, but here is my list of stuff I do and don't want to translate across from FFXI to FFXIV:
+ Skill Chains (Elemental)
+ Magic Bursting
+ Full Elemental Wheel
+ RDM, SMN, NIN, SAM, THF
+ Auction House
+ Relic Weapons
- Abyssea
- Slow combat
- UI
Also, I really dislike change for the sake of change. There is no point reinventing the wheel if something already works so effectively. e.g. Auction House vs. Market Ward.