A DSL such as you describe is orthogonal to something like outshine. There is no reason why you couldn't use both.
One of the main reasons I'm interested in outshine is for seamless use of org-mode in my emacs init files. While I suppose I could stick my emacs init files in a database and query it using some DSL, I personally prefer to have it in plain text and readable with standard text-processing tools.
One of the "common" (heh) solutions is to use org-babel to have a "literate programming" version of your .emacs that you then weave/tangle into the real .emacs
Personally, I've tried this approach with some smallish programming projects and literate programming has to be a good fit for your way of coding. Since I'm quite a big tester-rewriter, LP is a heavy chore. Of course, I'd probably get better doing it more often.
They seem to imply that no weave/tangle would be necessary with Outshine. At least I assume that's how it would work with the outline headings 'outcommented in the comment syntax of the major-mode language'.
I've seen org mode init.el files using babel, I honestly really can't see the benefit of literate programming in this way. It makes debugging so much harder than it need be.
I know everyone else that visits the site will have a larger attention span than I have, but it's possible that some will have even less than I have.