I suppose that what I can do (or any one can do) is get a copy of rebol.org scripts, then put them on github, work on code, correct bugs, accept pull requests, etc.
But keeping rebol.org in sync with changes in github repository may be difficult. I don't know, I have never commited anything on rebol.org, so far.
Doing it one way, from rebol.org to github is certainly easy: get a cron to run librarian.r regularly, and then git diff, commit, push, etc. But the other way will probably be more tricky.