I should also note that input.mozilla.org inspired MoodBar/the Feedback Dashboard extension (we actually met with the PM of the project several times before kicking off work on MoodBar/Feedback Dashboard), which can be used to collect feedback from users. We used it for collecting new user feedback on enwiki for some time, as well as enabling experienced users to respond to such feedback. You can still see it in use on nlwiki:
https://nl.wikipedia.org/wiki/Speciaal:DashboardTerugkoppeling
We disabled it on enwiki not because we think it's a bad idea, but because we'd ultimately like to integrate such micro-feedback functionality more cleanly with Flow [1] & improvements to the onboarding experience [2]. The "instant response" features in particular are difficult to integrate with talk pages in a way that's intuitive for new users, because talk pages suck for new users.
I realize you're asking for a general feedback mechanism for editors, and I too suspect that Flow will be the right foundation on which such mechanisms should be built. While I think input.mozilla.org itself is pretty sound, in the long run, we benefit more from tools that are well-integrated with the Wikimedia user experience.
Erik
[1] https://www.mediawiki.org/wiki/Flow_Portal [2] https://www.mediawiki.org/wiki/Onboarding_new_Wikipedians