The main reason they were banned was that viceroy's generally require the alliance to hand over root access to their forum, which could be considered theft.
However, viceroys existed in a time before alliances were a real concept faithfully represented in the game itself. I dislike the idea of viceroys, but as a thought experiment, I wonder if there is something worthwhile perhaps to exploring what could be legally done instead.
Now that there is an in-game representation of alliances, there could be a more in-game-focused hand off the AA.
If an alliance was required to relinquish control of the AA itself, then board owner would not need to hand over root access. This would also be an interesting way to enforce draconian peace treaties, because non-compliance could result in immediate termination of the AA or expulsion of offending members.
A softer method of vice-royalty could be the forced signing of a MDMA (notice no optional clause), optionally backed by AA ownership (to enforce in-game compliance).
This would enforce in-game alignment, but still leave the out-of-game properties to act as they please.
Still not sure its a good idea, but that's certainly an option for how to reconstruct viceroys. In general, use of the in-game AA ownership concept might be an interesting twist to peace terms or even protectorates in the future.