I’ll look for the post, but this has come up. Eventually there will be vaults that hold data so long and so reliably that they will be “promoted” to archive nodes. What all that entails I don’t remember, but as far as vault ranks go, that will be way up there. Again, not sure what all vault ranks will be used for in the future either.
Found the post:
It’s a big one, but has some great info in it.