Honestly, part of the reason for this is that I want to make a game!
I'm entirely unfamiliar with MUSH/MUX code, personally, and always felt they were handled a bit rough-around-the-edges. To make a game especially unique, I found it best to start from the ground up... and if you start with a code base that has much existing, you spend too much time/effort modifying/removing the systems that aren't right, which often results in breaks...
Better your than me, then! I set up the TinyMux code on my pc, and actually had a few friends playing, but it was a ton of work and mainly beyond my knowledge base (Brazil helped me a whole lot!)
The only hard part is nailing down the specifics - how stat systems should work, magic, and all that. If it's more roleplay-geared, than the majority of it (like fight code and all that) isn't so essential. As long as there's good support for dice rolls and folk to resolve disputes, it should give good grounds to flourish. I sent a message to Fred asking if it was possible to use the systems found in the DFRPG, and if so, that answers a lot of questions. If not, it still shouldn't be too troublesome!
As a player, I always found the Mush/Mux etc. a difficult environment, but I don't use it often and just don't remember the codes to make things happen. I'm 'way more familiar with the chat room setting. It's also a plus to me that I don't need anything more than my browser to play there!
But I was just throwing the idea out ... no problem ...