Rather than the D3-hardcore style, I'd prefer a more "classic MMORPG" style. Things like:
Takes much, much longer, like ten times longer to level. No rested bonus, no armoury bonus. This means all the level 10~45 crafted gear now will have a market. Level 1~49 actually matter now. You'd actually seriously consider melding your level 32 gear. Vendor food no longer have experience bonus, but crafted food gets 5% experience bonus.
Near-complete breakdown of aetherite network. The only form of teleportation that works is Return, and each Return will consume a materia (but will have no cooldown). You also may only set your Return point to one of the three starting cities. Chocobo porter network is however much more comprehensive, and you may take a chocobo from any station to any other station.
Death penalty: 15% of the total exp required towards the next level with level downs. No death penalty if you are Raised within 3 minutes; if not, then your body will disappear, and you will revive at your Return point with the death penalty; if you're in a instanced dungeon/raid, then you may revive with death penalties inside the entrance of the instance.
No token gear whatsoever. The current token gear becomes crafted using material from the appropriate iLv raid content (main material) and light party content (secondary material).
And zones scaled up at least twice their current size.