Now we can get a readable stream from the response, which is cool! But i think it needs a complementary WriteableStream for the request as well. Imagine being able to post more then what can fit into the memory or were you simply just don't have everything you need to post.

let ws = new WritableStream
let encoder = new TextEncoder
let writer = ws.getWriter()

fetch('api/upload', {
    method: 'post',
    body: ws
})

let uint8array = encoder.encode('chunk')

writeStream.write(uint8array)
writeStream.close()

But i guess the WritableStream has to be implemented first ^^