There should be moves to drive awareness to this on frontends. Like when peakd gives that popup that a new version is available. That same system could pop up on all front ends to say

A new version of Hive is coming. We need your help with testing.

A reward for finding errors could then drive actual participation. Simple tipping could be that reward but to make that the standard when new HFs are in the works would mean people take notice and each dapp/project doesn't leave it to the last minute.

It would seem projects/dapps are putting it off because it means work but then to not do it means the system in general might not work effectively.