It is theoretically possible to have a Rust port of Postgres support extensions. If you make all the relevant functions and structures ABI compatible with Postgres, extensions should work. The issue is the moment you're dealing with C pointers and C strings, pretty much all the code you have to write is unsafe.

They would need to be rewritten as there is no formal extension API. Extensions can call into almost any part of PostgreSQL.

They would need rewriting (a few are included)