[Ide]

I can think of at least two websocket clients (Decaf and phud) not to mention other text game 'clients' such as interpreters. All have issues with screen readers. It may look easy because it's 'just' a web page, but in my experience it's not that simple.

All of this talk about websockets is besides the point though. You already can use websocket clients to connect to muds that don't support websockets.

Creating a mud that takes connections (websockets, telnet, custom protocol, etcetera) is a relatively simple task. Creating a mud that other people want to play and/or use as a base for their own creation is another task entirely.

[Manitas]

Sure, attempts are made even though the standard is not yet established. Both are work in progress with some basic features.
It's quite normal for WIP to have issues, but there are no fundamental differences between normal websites and normal websites using websockets, so they can be made accessible if accessibility is one of design goals.

They are quite out of scope of this discussion, Decaf is client only, both rely on telnet and mud protocols and both clients are terminal emulators. Phud is an example of what i'm proposing not to do (in addition, it's written in PHP which is a bad choice imo).