The JS approach is still more cumbersome than a normal download, which just asks for a destination right when you click the link (if at all, I think most browse

The JS approach is still more cumbersome than a normal download, which just asks for a destination right when you click the link (if at all, I think most browsers default to just starting to download to a default destination nowadays). As for seeding, that would just happen while the download is going as you suggest, maybe have that configurable somewhere for the tech savy people. That would already scale quite well compared to no uploading at all with the traditional approach. The more demand there is, the slower the download gets, the longer you'll be seeding.. That being said, that's what would have helped 15 years ago, nowadays I'd agree that we're doing pretty fine with the centralized approach in most use cases.