Unfortunately BitTorrent is still heavily centralized when it comes to discoverability. Without a website hosting .torrent files or magnet links, it's very limited.
These links are easy to mirror, they probably fit into a reasonably large SQLite file. Since the Web still allows decentralization, that doesn’t seem to be a problem. For example, the pirate bay is blocked in my country, yet I can still consult it on dozens of mirrors.
Not at all, a DHT crawler can gather Torrent links over time in a fully decentralized way.
Without curation it's not worth much.
I'm surprised nobody has build a torrent catalog on bittorrent itself.
I think that with the DHT mutable item one should be able to publish a torrent containing a list of torrent with comments and updating the list easily.
It's not so simple. The juicy stuff is on private trackers and you can get into one only when invited. So you have a catalog of crap and not much more.