What's the most character customization you'd be okay with?

[Soukyuu]

ya i don't want tree specialization this is FFXIV and the key idea is you allow to play everything on one char.

Tree specialization doesn't mean you can't play every class on one char though. It only restricts a class to a certain setup, but you can still play every class.

Something like D3's skill customizing could be a nice option too. Everyone has the same skills, but depending on your playing style you'd choose from a set of effects to modify/enhance your skills.