I like the idea of building a MUD. If its feasible at the current state, i have no idea, but i hope you manage to build at least a proof of concept!
Regarding first programming languages, i think a good first programming language is one that has plenty of educational material, loads of previously asked questions on Stack Overflow or so, and makes sense for a given domain. I tried learning programming in the past but it made no sense in isolation, as i had no real reason to learn it. After finding myself in a business intelligence position learning things like R and SQL made sense because i could relate what i learned to what i tried to solve. I have no idea if you can get a bunch of middle school kids to get that connection with Julia. On the other hand, some folks worked on educational material for Haskell and it seems to work, so why not Julia.