I think it's time that we acknowledged that the biggest reason that "people don't test when it's alpha or even beta" is because it is too hard to try out betas.
Our package managers have ingrained the idea of "latest is greatest," but that breaks down when trying out beta software. Sure, I can try out the latest from rawhide (or unstable, or its distro-specific equivalent), but then my current version is removed, and multiple beta dependencies are installed. My system is either permanently unstable (from constantly fetching the latest betas), or frozen in time with no updates until all the betas become full stable releases.
Switching between beta and the release version is very difficult -- having multiple versions of the same software is rarely well supported. This is exacerbated by the difficulty of downgrading software.