For example, I think going forward we are asking for trouble having corrosion in EPP input repositories because it means that a package can pull in some deps from corrosion, even though they are available in simrel. e.g. corrosion's p2 repo that is in EPP input contains lsp4e, mylyn, gson, etc. This means that unless someone continue to ensure that the corrosion p2 repo has exactly the same version of each plug-in as simrel, we have situations where the EPP package can be built with artifacts not coming from simrel.
From Corrosion POV, what's interesting in EPP is that it brings some level of consistency with other packages, making users more comfortable when switching their target stack and their Eclipse IDE. Being fine-grained about which dependencies are coming from SimRel or not is not really that interesting; but I understand that this can cause an issue to other packages getting unexpected (&non-SimRel) artifacts.
At the moment, I don't have a concrete solution to this problem; we're missing a way to configure the build to always prefer artifacts from SimRel and restrict Corrosion artifacts to the Rust package.