Indeed, I agree! PHP was where I started and the user contributions in the PHP doc was priceless. We could solve that with Disqus (https://disqus.com/). Just jack in some JS when the refdoc is being run on pike.lysator.liu.se. I’ve already done that with Google Custom Search:
The big problem with user contributions in docs is that the quality
varies from "good enough to turn appalling docs into something you can
actually use" to "flat-out wrong and horrendously misleading". Is
someone going to vet all posts and make sure they're on the better
side of the scale?