I volunteered for a MUD for 3 years. It was much more popular than you'd think, MUDs have their own niche audience.
A lot of times small projects would be taken on by people still lower ranked working to prove themselves as they learned the internal code, etc.
I personally produced oodles of content while doing other things like building entire areas.
Now a MUD is different in the fact that even a popular MUD pales in comparison to Warframe, but chances are small changes can be made without destroying the entire process of development for other projects.