I imagine it would work like a CLA in a lot of company sponsored open source. You retain copyright, but allow the owner to distribute it under their specified license terms. Or you could have a CLA that actually assigns copyright.

The ongoing maintenance of the contribution is definitely an interesting question. That is the same with classic OSS projects too, though. I know a number of projects that are going towards making a pluggable core with plugins maintained externally to reduce this burden.