There are a couple of big pieces of work here:

1) Making the "cargo vendor" story work better. rust-url has a bunch of dependencies, and you have to get them all in-tree.

2) More security review & planning. URL parsing is scary! And we'd want to ship & run it alongside the C++ one to check for places where rust-url is not fully web compatible, but there are major privacy issues in reporting back anything more than "1 failure," even for users who have explicitly opt'd in to reporting back data.

But the team is definitely working on both of these pieces and I'd hope to see it in the near future. No timeline / release number promises, though, right now :-)