Vitess for PostgreSQL will probably just be... Vitess.
The concepts behind Vitess are sufficiently general to simply apply them to PostgreSQL now that PostgreSQL has logical replication. In some ways it can be even better due to things like replication slots being a good fit for these sorts of architectures.
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.