which of these mud settings interest you the most (r1)

I like #1 the best.
I don't feel it would be as restricting as some think.
Maybe possibly a long depleted asteroid mining station or an ancient station, built before the current races had FTL travel.
Leaves lots of room to introduce new stuff with it out being jarring to the setting. Using a asteroid/ancient station cliche can help maintain why resources are scarce, as well as secrets to uncover.
Some resemblance of society, with a massive underclass that's born, lives, and dies with in the stations ancient bowels. Few ships come by to trade, but very few if any ever can afford to leave.
The economy is held loosely together by whatever is salvageable. Major factions fighting for control over water/food resources.

Babylon 5 meets Armageddon sounds like hella fun I ain't going to lie.

First one to be sure but don't make it as slow as Atonement RPI.

Also rinth isn't that dangerous unless you are doing dumb shit or a mage.

"I've been down there. I'm not going back. Freeze me, anything... but don't send me back. Please man... I've seen shit... I've seen a Vore grab a man with four of its meaty arms, dismember him, proceed to scat on the gory remains, then do the same to his wife. Just for the hell of it. I've seen men who've gone blind topside when the electric storms were raging. You know as well as I. I've seen those hellish, night-black seas with waves larger than mountains. Ice and rock. Fuck. And those fucking trees. Those spores. We don't have the equipment for it anymore. We cant even make suits anymore. What have we got... a few old rifles and a can-do attitude? What the fuck are we supposed to do? Live down there? Its fucking impossible, Dan. Its fucking impossible and you know it."

"They did it."

"They have a seven hundred year headstart on us. They're barely human anymore. They're primitives. We don't have to live like that to survive, do we? Fuck that, Dan! Ship designs may have been the same but we can come to a better conclusion this time. We don't have to live like that!"

The man in the white cell looked at his reflection in a pane of black, one-way glass. An unfeeling, monotone voice broke the silence.

"You and your team have been assigned to the southern continent. Optics have revealed some sort of city hewn from a rock formation there. You are to blend in with the locals. You are to learn as much as you can about them - chief being population figures, leadership structure, and the location of their ship. Under no circumstance are you to tell them who you really are or where you come from. As you know, we can only monitor you some of the time. That is why if you do not come back to the pod within one month, the time-release poison in your bloodstream will be enabled, and you and your entire team will perish. The details have been transferred to your Eidolon. You have one hour to rest."

The options are kind of skewed. I wouldn't mind seeing any number of settings done well as an RPI. Anything from Star Wars to Vampires can do well as an RPI if it is setup, managed, and run right.

Something with player-made autonomous construction would be really interesting, like a deserted island or something. You could easily make some crafts that take time to progress and result in buildings, then all staff would need to do is convert the finished product to an enterable building and paste in the descs that players submitted. Might need some minor coding to do with keys and doors as the traditional way of dealing with that on MUDs doesn't really suit an environment where players can create new buildings regularly.

As someone who has reviewed creating a MUD and staffed for over a decade on others. I can tell you right now what any creative content creator or media producer will tell you. People do not know what they want. People do RESPOND to passion and quality. If you build it they will come and if you can't get everyone that is fine, you will get your market share. You cannot create a MUD by council or democracy. A MUD must be created by a clear vision and a leader who can convey their vision to their staff.