...like defining /mediawiki/skins/ as a project so with one click you can filter on any related activity in all skins.
Would have to happen via project.json files to create. Cannot do this ourselves until Bestiary tool is in place.
Note that projects are not disjunct I was told: two projects could contain the same repository.
T179240 is a potential usecase here (one project = one engineering team).
Discussed this idea at FOSDEM 2018 with Bitergia.