WebTorrent should just work on a browser, no special client necessary. This will allow projects like PeerTube to create websites where the primary content is decentralized by viewers kind of thing.
You close browser = close WebTorrent = you stop seeding
You stop watching video = you stop seeding it
Long and large video file? = if most people watch at half of video, then data from beginning is already out of the buffer = no seed for first half of video.
To this day there is still no support for WebTorrent in other popular Bittorrent clients so they can't connect to each other. But there is some movement in libtorrent library so we will see.
A quick glance at the webtorrent readme says it uses UDP on node.
There is a webtorrent desktop app in beta that does both.[0]
Here's hoping it makes it to libtorrent. Even then, I'd imagine it would take quite a while to make it into the clients running on seedboxes, desktops, etc.