I genuinely like this idea, because it would allow to reach both goals.

The problem I see is that this would probably go down the same as the bodycam idea, with inconvenient recordings vanishing due to "technical issues".

You'd need an independent third party doing life recording and delayed release. Subjectively, the US don't have a great track record with these.

Easier idea: Just publish last week's encryption key. Probably won't happen because some tech supplier will lobby for a more expensive solution.