I'm really not sure if modernizing MUDs is worth the effort. Actual MUD gamers will look at it with either contempt or distrust, especially blind players. And regular gamers are unlikely to play a text game. I could make a game with a MUD sensibility or even use a MUD engine, but I would never call it a MUD. MUD players want more of the past and I'm not really interested in that.
Isn't accessibility for a web-based MUD just a matter of adding `aria-live="polite"` as an attribute to the incoming text? Five years ago I did this on https://evolvingstory.juliablewis.com/ and it seemed to work with OSX screen reading.
And they don't wanna be left behind. They wanna use their own client on a telnet connection because that is already suited for them. Many QOL features for the sighted can have a negative impact on the blind. Any attempt at engaging that audience must first convince them that you won't leave them behind.
One simple way to benefit the blind is by making sounds integral to a game, with clear cues for everything.