I don't think future ranking adjustments are a bad idea. I imagine that every 10 year old Legendary on this forum could be given a new rank in the future "Legendary II or something" especially if they have achieved a certain number of activity and merit.
That's been discussed before, amongst others in
Evolution of rank names and
What if Theymos added new Rank after Legendary?.
I'll repeat my suggestion:
I'd say just "Legend" sounds good. Or maybe just add a bold font to the current Legendary rank.
-I vote for the name Legend. It's simple, and makes Legendary look a bit like "Legend-ish", while Legend sounds like "the real thing".