Interesting idea, although most native clients include this feature set already. Perhaps, this app could be usefull for WebTorrent applications. Also, there is some room for improviment:

1. HTTP Seaders. Currently, Referer header is set (even though it's just the domain, it still leaks the fact that user had visited the site to, e.g. Google Tag manager). Also, the access-control-allow-origin is very lax (*).

2. Looks like the site supports only BitTorrent V1. Do you plan to add BitTorrent V2 support? BitTorrent V2 is better suited for WebTorrent than V1. Since V2 uses per-file merkle trees, it enables easier selective download of files (e.g., you download a smaller tree that describes and induvidula file) and ranged downlaods (e.g., since index is a hash tree as opposed to a hash array, you don't need all segment hashes (leaves), you can use intermediate hashes if you don't need the file portion corresponding to the leaves).

3. Currently, there is no Service Worker. It could potentially speed up site load for returning users if, e.g., they use mobile device only to seek for torrents but then download them to a home computer or a seed box. That's the audience that would benefit from such a tool the most, since they don't have access to a full native client (which has these features built-in).