I am aware how bodies are streamed in HTTP/2 (I have written an implementation). What I am not sure about is how libraries on client and server side are expected to handle this kind of information. A Lot of servers and client libraries might display "transfer-encoding: chunked" to their user, even though that wouldn't be seen if the connection was established via HTTP/2. It's more of a question of "how to hide those protocol differences from the user while still allowing them to set and access all information if required". And the question whether the HTTP ecosystem already embraces that, or whether most libraries still expose all the HTTP/1.1-only ways to the user.