Legendary already takes several years to obtain. I feel like this is enough. Maybe if I someday start to see that there's some decently-sized subset of Legendary members who are "noticeably more veteran", then another rank would be appropriate.
I'd rather see a rework of the high level ranks. The required levels of posting are almost non existent so at the moment its simply a "who has the oldest account" game. For example, Legendary requires ~1000 posts over 1000 days....