I like the current format because it keeps the tagset tidy and that makes my brain happy.

Suggestion: To minimize the concern about tag lengths, you could do initials instead of fully spelling out the words "character", "relationship" and "worldbuilding". For example:

C: Leia Organa (OT)
R: Leia Organa & Luke Skywalker (OT)
WB: Bespin gas extraction (OT)



"However, it means no canonical tags can be used, which means every association of tag to fandom has to be approved as well." Don't all tags to fandom have to be approved anyway?