Would a modern MUD be web based? What is the modern web version of a MUD?
I don't think immersive 3D like the aforementioned WoW is really a MUD but I am not sure pure text is to my liking. I think Rogue-likes might have hit the sweet spot — allowing you to explore somewhat graphically but there was still a degree of imagination required. The cost to create a Rogue-like world too would not be prohibitive (and I mean cost in terms of time and effort — like the time and effort that would be required to create a 3D immersive universe like WoW, etc.).
And, sure, I know Dwarf Fortress is a thing but the other aspect of MUDs that was cool was that so many existed with their own unique feel and character.
I guess I am looking for a web ring of Rogue-likes.
Even cooler if, while on different servers, they had a mechanism for linking or tunneling to other sites. I'm imagining two sysops cooperating and adding tunnels between their two worlds so that a player could wander into a completely new world — unknowingly moving from one site to another. You get enough sysops to join up and you kind of no longer need a web ring.