Some of the changes necessary were too invasive/breaking to gliderlabs/ssh, such as https://github.com/gliderlabs/ssh/pull/161 so making a copy ended up making more sense, I think. That's my understanding from what Mohammed's told me, anyways.
The maintainers gliderlabs/ssh have plans for a new version with more ergonomic APIs but the work hasn't started yet. I didn't want to wait either.