See https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2....
The specification makes gRPC sound rather tightly bound to HTTP/2 level details, but I don't think it really is. You should be able to speak gRPC just fine over any kind of HTTP. One main pain point for browser support however had been APIs to exchange trailers, which are necessary for gRPC.
The headers frame, and the capability to have headers before AND after content is a requirement. gRPC requires trailing headers for the status code of the call. Trailing headers frame is a new concept in HTTP/2.
gRPC-Web supports HTTP/1.1 and browsers. It is able to do that by encoding the status into the end of the response body. However gRPC-Web is a different spec.
If HTTP/3+QUIC supports the same features of HTTP/2 then gRPC should work on it. There might be a HTTP/3 specific spec for details around the management of a HTTP/3 connection, but gRPC headers, message content, and proto contracts shouldn't need to change. Take what I say with a grain of salt because I haven't looked closely at HTTP/3+QUIC yet.
Therefore the fact that there is a frame involved doesn’t really matter.
HTTP/3 doesn’t change the HTTP semantics: Peers are sending 0-N informational headers, 1 set of request headers, a stream of body data, and 0-1 set of trailing headers. Therefore gRPC should run fine over it at long as the underlying HTTP library exposes all those necessary features.
