as promised I've just published the PE and the PE4MPS projects.
You can find a small overview and the links to the github projects at this blog post: http://mar9000.org/bliki/a-grammar-for-projectional-editor.html
The two projects are in e very early stage, nevertheless I think the overall idea is already there. I'm quite new to MPS and onestly I'm not sure this work can leads to some remarkable value.
In case I keep working on this expect some more questions on this forum.
Feedbacks are welcome! :-)