MU isn't the same as RPG via Discord, Roll20, etc. MU isn't what they do on Critical Role, Harmon Quest, Geek and Sundry, or other gaming podcasts, shows, etc. If they want to do the thing that Terry Crews, Patton Oswalt, Deborah Ann Woll, and the people at the store that sells D&D products are doing...then you're probably doing them a disservice by suggesting MU.
IMO the only people who should have MU suggested to are people who are (ex.) "looking to primarily do writing online".
I think it's pretty honest to say that Mushing is not a place where youre going to get the tabletop RPG experience. MU originally started as an attempt to do exactly what Roll20 is doing right now in a much more user friendly format. It has since become predominantly focused on creative writing, but uses antiquated programming methods that turn getting involved into what could result in days to get involved (long application processes), learning curve on commands (shell-script style command functions), and requires you to log in to hunt and find writing partners. A lot of these things mentioned have been rendered obsolete by other modern services, which is why it's simply not attractive to younger generations.
- Advertise as a writing hobby and not a gaming hobby
- evolve to web-based formats that are more user friendly
- wikis are great
So, in summary if you're looking for new blood in mushing, I suggest you look into people involved in online writing groups like slashfic and fanfic writers. Those people might love it and stay, but when people want TT RPGs they're going to eventually find that this hobby isnt what they're looking for.
Also, if the community wants to be more attractive to new incoming players, the snobbish, paranoid, salacious, and cliqueish habits need to come down quite a bit(1). I've known plenty of players who have left the hobby altogether (or shortly after trying) that quit the people, not the format.
(1) There are plenty of nice people, if not a quiet majority. However, the existence of people harassing others for TS, snobs thumbing their nose at people with cliqueish behavior/culture of judgment, and getting paranoid and avoiding new people because they might be that one guy or OMG their IP comes from the same state definitely can drive good, sane, and normal people away from the hobby.