Please! There is a working TypeScript client implementation [0] of gRPC-Web [1], which relies on a custom proxy for converting gRPC to gRPC-Web [2]. Would be nice to bring that proxy functionality into Nginx.
Armeria [0] supports pretty much every possible combination of gRPC variants, including gRPC-Web - HTTP/1 and 2, TLS and cleartext, Protobuf and JSON, framed and unframed.