The markAdmins gadget is on 34 wikis (default on 3) and used by 2,712 active users (21,160 total users).
Is it worth turning it into an extension? (This is part of T177674: Investigation: Short-term solutions for global gadgets.)
Lots of these scripts seem to manually list the admin usernames; the Commons one does it differently. Perhaps the easiest solution is to load the commons one on other wikis?
The wikis are: