Okay be prepared for the tangent here because this is one I've thought about for quite some time .
1. What races would you allow?
I tend to prefer human characters at start up, if there were other races they'd need to be carefully researched etc in terms of abilities and gains and different playing styles (think lament), but human baseline is often easier, especially at character startup, particularly because I am not a fan of muds where your limited by profession or race selection on what skills you can learn or what activities you could do.
2. What professions or classes? Or would it be a Mud where everyone could gain whatever skills they wanted without classing?
I always prefer the clok style system of gaining skills through use. That way if your board of combat you can go and try something else and aren't tied to one specific activity, or weapon or set of skills.
3. What theme would you like? Fantasy, historical, space, or something all your own?
I've always been intreagued by those worlds that mix sf and fantasy together, like anne Mccafry's Dragon riders or Robert Silverberg's majipoor. So I think I would probably set the mud on a newly colonised planet, one that still has a lot of wilderness and need for basic skills, perhaps even with some sort of native medeival society, but one where there occasional spaceships, robots etc to give a change of perspective and atmosphere.
Oh and yes, I really! enjoyed Wayfar1444.
4. Would you have combat, and if so, how would you make it unique?
Yes, i would have combat, but only for specific reasons or in specific areas, eg, a hunter would need to hunt and kill their prey, and someone involved in fighting hostile aliens or creatures would need the skills for that, however players would not gain xp specifically for each kill, though they may gain xp through use of combat skills.
5. Would you have crafting? If so, what crafts?
Yes, crafting would exist as part of the new colony ethos, however since the game has the potential for futuristic technology, what sort of crafts happened would change as players progressed through the game, eg, at the start a player would need to make their own clothes by weaving their own cloth from wool, or flax or tanning their own hydes, however later on players could start farming plants for the components to make synthetics.
6. Would you let players build their own homes? Areas? Planes of existence?
The idea behind the game would be establishing a new colony, getting on and trading with the natives, and getting more citizens, so there would be a lot of building going on, perhaps even with managing npc colonists.
7. If your Mud wasn't combat oriented, how would you let characters level? What goals would you set up for them to strive for?
The object of the game would be first to go through the wilderness and survive, then to setup a colony, then to managie your colonists.
As part of this you could have various tasks and goals to accomplish, from trading with natives to fighting off space pilots or building a spaceship to get supplies from other worlds.
The key difference is that there would be quests and npcs to interact with along the way, and development would happen slowly. So instead of typing "farm field" and expecting to get stuff immediately, you might have to wait for your crops to ripen and to be able to harvest, one reason why you would have npc colonists to automate some tasks for you, though of course you'd have to make they were also fed, clothed, housed entertained and generally take care of them.
The game would alternate between you managing your colony, and going out into the planet either on npc generated quests, given by either the colonial authorities or by local natives, or even quests generated by your eg someone might become seriously ill and you'd need to first ask a native healer where to find the necessary plants to cure them, then go and find said plants, and maybe even have to fight off bandits or beasts along the way.
The game would balance doing these quests and tasks and crafting and managing your colony, indeed those players who prefer not to do combat, you could even potentially have npcs to send on quests or to perform tasks for you, for example if you heard rumours about a gang of marauding space pirates who were exploiting the natives, you could either go yourself or craft the weapons and items to outfit a fighting force of npcs from your colony to deal with them.
Oh, and there would be absolutely no, zippo nada pvp whatsoever, since the focus of the game would be on expantion, indeed I would suggest that your colony and the land it takes up is effectively not part of the main wilderness map, so only you, or any selected friends could enter it, rather like dwellings in other games, though manifestly there would be a lot of stuff going on there such as farming, building factories, outfitting npcs etc.
I don't suppose anyone will ever make a game like this, but I thought it was a fun idea .
With our dreaming and singing, Ceaseless and sorrowless we! The glory about us clinging Of the glorious futures we see,
Our souls with high music ringing; O men! It must ever be
That we dwell in our dreaming and singing, A little apart from ye. (Arthur O'Shaughnessy 1873.)