Oddly, following the Wikipedia list of different programming paradigms to "language-oriented programming" led me right back to MPS, and a raft of fascinating articles by Martin Fowler about the notion of a "language workbench". [Here], [here], and [here].
Chief among the things that people seem iffy about in LOP is the idea that the stored representation is in fact no longer text (and what that does to version control) - but you know what? Decl is probably an ideal representation language for a DSL-oriented approach (one of the things I was struggling towards in the first iteration) and is entirely text-based.
So that begs further exploration.