Really? I thought this process to be like in Debian, where an app in testing might not make it to stable yet, but won't be demoted to unstable if it has a 'testing' quality.

In practice this might make life of testers easiers, having extras-testing activated in their devices but not extras-devel, and till having somewhat functional devices themselves, avoiding to see apps disappearing when they update.

Therefore a package would disappear from extras-testing only when a more recent version substitutes it? Unless the package is so buggy that must go back to devel.

I think a new version would reset the evaluation of a previous version no matter what. This makes developers prepare better their releases, saving not onle extra evaluations of minimal changes but most importantly saving downloads and updates of minimal changes to end users.