A rare mention of Intentional Programming aka IP (https://en.wikipedia.org/wiki/Intentional_programming) on HN. I first came to know of this from an article by Charles Simonyi titled "The Death of Computer Languages, The Birth of Intentional Programming" on MSDN. But alas, the promise never came to pass. The only other place i know of which covers it is a chapter in the book Generative Programming Methods, Tools, and Applications by Krysztof Czarnecki et al. IP is rather hard to understand (i still don't get it completely) and afaik there are no publicly available tools/IDEs to learn/play with it.
I don't believe Jetbrains MPS is a IP programming editor, it is meant for designing DSLs. IP has aspects of a DSL but is not the same.
Finally a huge upvote for mentioning Markus Voelter who is THE Expert in DSL design/implementation/usage. Checkout his articles/essays and the free ebook "Domain Engineering: Designing, Implementing and Using Domain-Specific Languages" from his above mentioned site.