I think traffic shaping is very desirable when using a websocket for a separate command-channel. The last thing you want is an upload blocking all communications over that command-channel.
Furthermore, browsers can open only a maximum number of connections at the same time (I believe the maximum on some browsers is even just 2). What if the application already uses one connection for a websocket? Will there be only 1 connection left for the upload? And what if the browser needs to download other resources in the background, such as images, fonts, etc.?
Some valid concerns indeed! You may run dedicated uploading infra which allows more connections (different subdomain/IPs), but it's something we want to be explicit about in our developer guidelines, I'll also see if we can make traffic shaping part of the js browser implementation, as this seems to need it most - thanks!
Furthermore, browsers can open only a maximum number of connections at the same time (I believe the maximum on some browsers is even just 2). What if the application already uses one connection for a websocket? Will there be only 1 connection left for the upload? And what if the browser needs to download other resources in the background, such as images, fonts, etc.?
Just some concerns, good luck with the project :)