There's a section in the readme describing vector space https://github.com/pgvector. . Also, the maintainer is actively working on product quantization https://github.com/pgvector/pgvector/issues/93

Supabase was also asking for sparse vectors https://github.com/pgvector/pgvector/issues/81

Speaking of the repo, they have a number of features they want to add if anyone is interested in contributing, there's lots of room for advancement. Many of these features already have active branches https://github.com/pgvector/pgvector/issues/27