Are you planning to release custom languages built inside of Jetbrains?
Here are some that I've heard of:
- Swing UI lnaguage
- Web Applications Language
- Prolog-like language
- Diagramming languages
- Packaging Language
- SQL support
I didn't find these in MPS Beta 1 distributibe nor in wiki at http://www.jetbrains.net/confluence/display/MPS/MPS+Languages+Repository
At least, it will be really useful to have a single location for all existing/planned languages (open-source, commercial, educational, etc.). It will be kind of marketplace or advertise board both for developers and MPS itself.
Maybe something like IDEA's plugin downloads window.