[raesene3]

Ah yes, so the threat model for developer signing is compromise of the repository. So here we're looking at the OpSec of the repository owner (e.g. PyPI, npm, Rubygems etc), and also the risk of deliberate compromise by the repo. owner (for example where a state with authority over the repository compels them to modify a package)

In terms of compromise there's already been the attack on Rubygems in 2013, but in general the thought here is that these repositories are extremely tempting targets for well-funded attackers. A compromise of npm for example would give an attacker direct access to a very wide range of targets.

Combine this with the very limited resources of the repository owners (most are free resources, likely constraining the money available for defence) and you get a realistic risk of attack, which is mitigated by an appropriate use of signing by the developer.

Docker hub has deployed an implementation of the Update Framework to address this, although the interesting point now is whether people actually use it as it's not compulsory...