It will probably be *hard* and may take a while to implement *if* they ever consider it. But other MMO's have done this before, so I wouldn't say it's impossible. But with Yoshida saying everything has a *quote* 'data limitation' *end quote*, we may never see this happen.
But IF, just maybe IFFFFF we can get a raid server where anyone from any regional server whether that be JP\NA\EU can join can play... this will possible create a much larger end-game raiding community.