T12493: Setting a temporary usergroup (allow expiry of user rights via Special:UserRights form) is about allowing local user groups to be assigned temporarily. This was a top-10 wish in the 2016 Community Wishlist Survey.
A logical extension of that wish would be to allow global groups to expire as well. From a quick glance, it looks like the CentralAuth code and tables would need similar modifications to core code and tables.
It's worth noting that the community discussion at the Survey didn't mention global groups. However, it seems that this could be useful for global IP block exemptions among other things.
There are only 8 temporary group memberships in force at the moment (6 GIPBE, 1 global delete, 1 global editinterface), so this doesn't look like a high-priority task.