If you built two impls, your compiler wouldn't know which to pick. Or to phrase it differently, if you wanted to be able to choose the right one, it wouldn't be 'orphan impls', it would be 'orphan impls plus some selection mechanism'. E.g. Scala implicits. And once you have Scala implicits, non-orphan impls probably start looking like a pretty sweet alternative!

It absolutely should be relaxed for workspaces.

Workspaces are a great way to architect larger projects and monorepos, and they'd at least be internally consistent.