I really like the idea of a Discourse topic. Something like the “PRs in distress” series, but instead we link to PRs that remove packages. People on unstable that want to get a heads-up can then simply subscribe to it.
There are still details to discuss like whether those PRs should be open for at least X days to give people time to react, and whether all package removals should be posted or only “mass removals”. I think either way that thread would be rather low-traffic, but that’s actually a good thing.
Edit: let’s try this out! Breaking changes announcement for unstable