I think this will be very useful feature. I often get buffering because of my upload speed sky rocketing, or my home networks hogs because the same happens with my download speed. I know popcorntime depends on people sharing, but you can set minimal value for upload speed, like 100 kb/s, which will ensure that everyone is sharing.
Webtorrent (the torrent client used in PCT) don’t have speed limits features for the moment.
To be implemented in PT it need first to be implemented in webtorrent.
There are often patchs submitted to add this feature to webtorrent but apparently it isn’t reliable or satisfying enough and they never merged it into the code.