Project information: A multi platform Twitch.tv browser for Streamlink
Name: Streamlink GUI
Homepage: Streamlink Twitch GUI
License: MIT License
Upstream has been contacted: Not personally but they have a FAQ that states they are open to a Flatpak which can be seen here Installation · streamlink/streamlink-twitch-gui Wiki · GitHub
Streamlink Twitch GUI, oh yes please. So weird this is still not done. Package all together inside one package what one needs to easily install and start watching Twitch.
There is no official Twitch app for Linux and the Gnome Twitch project is dead. This Flatpak should be high priority IMO. That all said the Twitch.tv page is one of the most heaviest and awfulest there is and they are not going to do anything about it.