I think that for the first step, we need to make sure that AOSP forks can work. And those can just copy the binary blobs.

Don't get me wrong: I like all alternatives. But the most realistic alternative to Stock Android is based on AOSP. In good approximation, today nobody would want anything else.

If we get there, then the next step is to get open source firmwares. But I don't know much about that and it feels like it is a much harder fight. Hardware manufacturers probably strongly believe that they will lose their competitive advantage if they open source their firmwares, and I don't know how true that is.