Hmm I see but where would it be best to take priority? What if that person has 10 different secondary groups set?
Thats the problem . . . though this addon's true potential is in the fact if you can get it working with xF's automated promotion system(it is a real shame that the promotion system doesnt effect primary groups).
Well the way I can see it is this:
Secondary groups don't take primary over each other, so I have three secondary, Bronze, Silver, Gold, and I give them all to a user, then that user will have them all on TS.
What you can however do is. . add an option to silence the primary usergroup and then I can handle everything via secondary, and those that don't have a need for a system as dynamic as ours can still use Primary and make combinations. Maybe users can use both primary and secondary if they don't want to mute the primary user group.
Edit: Let me know what you think.
Edit 2: instead of making an option to ignore primary usergroup, just don't attach an id to that group and all you would have to do is create the ability for it to use secondary groups.