After getting this error message when trying to create a new tag synonym for 3d-view
Failed to propose synonym:
Version specific synonyms can only be created by moderators
I researched it a bit and found that (it appears) SE does not allow anyone but moderators to create synonyms for tags with numbers in the name. Why?
I have not seen any problems with version specific tag synonyms on BSE. If it is a problem on other sites (SO) why not make the synonym lock only for those sites.
Further if it is found that the tag synonym ban is really be needed on all sites, why not have it be another part of the privilege system? Say if you have the "access to moderator tools" you could then propose a tag synonym with a number in the name (providing you also have the needed 5 rep in the tags.)