You can still on the current Apple TV. In fact if your app is just full of video content or similar then you probably should.
Re:On Apple's Love Affair with Swift
by scarface74 on Sunday August 12, 2018 @03:23PM
(#17745966)
Wow. That looks easy.....
https://www.raywenderlich.com/372-tvos-tutorial-using-tvml-t...
Plex was ported to the 3rd Gen AppleTV as an unofficial app just by running a server on your computer and redirecting DNS to it.
https://github.com/iBaa/PlexConnect/wiki/Install-Guide