Winding down my Debian involvement
The last few years, my current team at work conducted various smaller and larger refactorings across the entire code base (touching thousands of projects), so we have learnt a lot of valuable lessons about how to effectively do these changes. Notably, the cost of each change is distributed onto the package maintainers in the Debian model. Debian is lacking tooling for large changes: it is hard to programmatically deal with packages and repositories (see the section below).
Source: michael.stapelberg.ch