I wouldn't want to merge FFXI and FFXIV any more than I'd want to merge ANY of the Final Fantasy games. They are all distinct, unique worlds (with a few common elements), and should stay separated.

If FFXI is to live again, it should be as a sequel game, not by shoehorning it into another game. And I don't actually think a sequel to FFXI is actually wise or necessary. The game had a good run, it's over, and for the time being it's still there for folks who want to enjoy it.