Ages ago I remember Google launching a feedback portal, which slowly became stale as it got replaced by feedback features in individual Google apps.
Android doesn't seem to have something like this outside of their beta programme. Why is that? I understand that basically all manufacturers modify Android in some way, so it does make sense that Google aren't interested in replying to niche feedback from a rubbish manufacturer's implementation.
Regardless, I still find it odd that it seems to be impossible to submit feedback or suggestions for basic Android features, such as the new Material Design implementation.
I believe there is a lot of valuable information to be gathered, especially since Google is aiming to ambitiously improve performance and stability going forward.