Since the Merit System was set in motion(*), 182 Legendary members (48 from scratch) have ranked-up needing Merits in the process, and 173 Heroes (71 from scratch). Not that many considering (besides all those pre-Merit System ranked members also existing).
There could be room for additional ranks, although I wouldn’t say that there is any seemingly good reason for it beyond elevating the ego of those that would meet the requirement, at most. Currently:
There is an argument for adding additional ranks below Legendary and not grandfathering people into the resulting higher ranks.
1000 merit isn’t easy to achieve and not many will get there. 400-500 is much easier and more will earn this much merit. There could be some criteria to adjust the initial airdropped merit downwards and some working towards getting legendary status could need to get less merit, while those with a lot of merit could have a higher rank.