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.
It does seem like there are some issues for people getting hive keychain properly setup for testnet. I'm waiting until that gets sorted out and a nice video published walking through how to do it
AFAIK the issue with keychain is the modified version has to be accepted by google (it can be installed from github now, but most people don't know how to do that) and the timing of that is out of the dev's control. At least we shouldn't have to worry about this issue on the next HF.