I don't wanna be lighthearted nor do I wanna encourage you; the thing about your idea is simply - appealing on so many levels.
And now what?
We've all heard about so many different indie titles. I don't wanna imply any royalties are bound to their names, simply because those are not lucrative businesses. Altough MMO is the coalmine of the present, I agree on
jim's assessment regarding decades old MUDs at the internet's counterpart - your neighbor's BBS. Recalling that, I can only picture them as brilliant and fun - and even though from today's perspective that opinion "ain't for real" , MUDs were ahead of their lifespan and are stuck to just as many hearts as you can imagine.
Now, let's look at that difficulty curve from current perspective. The way I perceive it, majority of indie titles follow this logic:
Challenge --> Modding --> Expansion --> Modding --> Challenge --> Modding --> Expansion --> ...
This obviously lacks structure and flair.
That MMO game that's in my mind now, the one you've begun with, would have to feature a much better equasion; only then should an average RL player attempt to solve the problem that the proposed game has to offer. Instead of playing one RL title on his desktop and another two indie (or $$) MMOs online, he would probably leap into a dungeon to solve with his friends.
Let's expand on UnReal World, shall we? It's a perfect setting for a community-driven game. Tribes, territories, complex skills and simple economy revolving around items and services - you could easily drop 100+ players into this nordic setting. I asked myself more than once - why isn't it the case with this game, why isn't it spinned and made into multi-fun?
Can anyone on RT answer this question?
If I was to pick another MP or MMO title, with or without a leash keeping it with a social network, the answer would've been fairly simple -
someone had an idea how the game would look like right at the instance when it reaches the optimal number of participants. So, what are those players doing in "our MUD re-creation" six months from its release? Are they joining efforts to overcome an obstacle on so many levels that it can be tracked only via XP pool, or are they slamming into 99th dungeon level, spawning for the fifteenth time on the surface? Are they flooding their IM for someone to give them a hand in-game, or are they starting to grind resources simply because they've bailed out of that same effort?
It's not a murky, torch-lit vision of yet-to-come mediocre game title; it's a note to anyone's attempt towards designing a challenging, effective, branching difficulty curve
which exists just because the game is in essence a MMO roleplay.