We'll be integrating other indexing in near future (such as faiss), Annoy is just one option for indexing that was implemented. Each indexing method will have their pros/cons, so you'll be able to select the search engine backend according to your restrictions.

There are many reasons why we depart from other libraries, many of them, for instance, uses JSON+base64 (http/1) for serialization, while we use protobuf+gGRPC (http/2).