Prepper was requested a few times, and
eventually accepted.
Superuser is in a few dictionaries, mostly defined along the lines you outline, RTT. The Cambridge Dictionary gives a different meaning:
someone who knows a lot about a computer program and can help other people to use it
Most of the usage examples I found were of the system administration sense, but I spotted a couple with yet a third meaning: simply, someone who uses something a lot. Thus
The Atlantic in February this year had an article, "Facebook Has a Superuser-Supremacy Problem". The article says of these "superusers":
They are part of an elite, previously unreported class of users that produce more likes, shares, reactions, comments, and posts than 99 percent of Facebook users in America.
They’re superusers. And because Facebook’s algorithm rewards engagement, these superusers have enormous influence over which posts are seen first in other users’ feeds, and which are never seen at all. Even more shocking is just how nasty most of these hyper-influential users are. The most abusive people on Facebook, it turns out, are given the most power to shape what Facebook is.
(Why am I not surprised?) Also, CNET in April had an article headed "Washington State Program Wants Gasoline Superusers to Go Electric", with the subheading:
These superusers represent just 10% of drivers, but use over 30% of the total fuel. Can they be persuaded to switch to EVs?
Anyhow, the word is definitely out there. I'll add it as a rare word.
