One really nice aspect in MPS is stylesheets as a method of controlling the visual output of an editor, without making changes to the editor itself.
To this effect, would it be possible in a future version of MPS to support user-defined stylesheets? It could be used to allow a user to override a language's default color scheme with one of their own, or perhaps eventually such as letting each user on a project specify the curly-brace style they like best in a C-like language, without each changing the base stylesheet. (In my scenario, I just want to set a border around GText elements, to make it more visually clear when I use a whitespace-only GText element)
I know this is too late for 1.0, but this would be a very nice feature someday. :-)