So far, we seem to have a mixed reaction. Yay!; The TEI wiki samples page is better; other people already do this.
I do know TEI By Example, and it's good. It's a very different approach though, and much more opinionated and holistic. Contribution is via contacting the authors. What we had in mind was a much more open approach, building off the contribution mechanisms already supported by GitHub. The thing about linking back to projects (not that it's in any way a bad thing to do so) is that those sources might move or go away in time. I think there's great virtue to copies, especially when those copies are versioned and can be updated. I also think this might serve as an alternate archive for project data.
So I don't see this as competing in any way with those other efforts. As Dan says, I'd rather find synergies.
It is a bit of an experiment though, and one that probably won't work if the community doesn't see value in it.