It's already open source, because GPL requires it. It's unlikely to be accepted as an upstream contribution given that Oracle has their own Vector type that is only available in their MySQL cloud service. Don't expect it to show up in a standard Oracle MySQL community release.
There are no plans right now.If the Postgres community (or a Postgres user) would like to take this project up, the best way to proceed would be to do it as a fork of Vitess. Once the implementation has been proven in production, a “merge” project can be planned to bring the fork back into upstream.