Current concerns are the scaling and recall performance.
The author is looking at product quantization along with other ideas: https://github.com/pgvector/pgvector/issues/27
More details on product quantization: https://mccormickml.com/2017/10/13/product-quantizer-tutoria...
A nice repo that tracks the ANN relative performance of different indexes: https://mccormickml.com/2017/10/13/product-quantizer-tutoria...
Also shoutout to Weaviate because they have great docs, are open source and have very informative YouTube channel.