I like your logic here. Torrent index -> alternative platforms -> YT proper.
Assuming the torrent index becomes decentralized, there are really two categories where it makes sense to build this in:
The YouTube frontends, as you mention
The self-hosted downloaders that already exist, like Tube Archivist
I think the second category is where you get all the seeding traction. Sure, it would be great if the Android frontends also participate, but there are thousands of NAS devices that are already downloading YouTube videos for a single user. If there was an addon that allowed all of these users to share content automatically, I think there would be a lot of buy in / seeding.
