No, things don't need account-wide. Wanting to play different characters or RP as them outside your main on an MMO where you can do everything on 1 character isn't a valid reason to enable account-wide sharing. Or else they would already have it. All other reasons are irrelevant. For instance - "They want to experience the story fresh again" - They have NewGame+ for that. The only people complaining about the account-wide sharing are individuals who can't stay on 1 character to save their life. Again, you wanting to RP as a different character or look as someone new instead of buying a fantasia - isn't a valid reason. As for OP's problem with different data centers - Well, some of you unfortunately are going to have to give up something.

On a side note - it's unrealistic as you stated. Why? Because SE already stated in previous live letters it wasn't going to happen.