I haven't looked at what they're actually collecting, but here's a few things that come to mind:
- Time to install packages
- Versions of things
- Has the compilation (when required) failed? What dependency versions are installed?
- CPU architecture
- OS version
...
There's a lot more that can be sent from the client that's not available on the server side.
> I fundamentally don't 'get' what richness they actually need.
That's fine. Perhaps you could ask them instead of ranting about what you don't know or don't 'get' in a public forum?
> to know their software works for their users
Sounds like you're not very far from understanding why they want better telemetry.
> Prior to release (...) and you know anything less will work too.
Things break in unexpected ways. OSs are complex systems and there's a lot of interactions between components. Homebrew's user base is enormous and very diverse. There's 2 different architectures, many OS versions, lots of environment variables that might be set differently in each user's systems, different versions of libraries, ... I could go on but I think you get the picture.
Edit: s/collected/collecting/