Rust doesn't let you write an impl a trait that wasn't declared in your crate for a type that wasn't declared in your crate. At least one of the two needs to be locally declared. This makes splitting projects into multiple crates harder than it could be, but on the other hand it makes the crates ecosystem less brittle than it otherwise would be.
replySome people propose relaxing this rule for "workspaces" (local projects with multiple crates that are not published individually). I haven't researched whether that would be technically feasible.
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!
replyIt absolutely should be relaxed for workspaces.
replyWorkspaces are a great way to architect larger projects and monorepos, and they'd at least be internally consistent.