[_wmd]

"All problems in computer science can be solved by another level of indirection"

Since you can easily fit the Magnet hash in an OP_RETURN value, all required is to move the torrent's description (title, description, categories, magnet URL) into a torrent of its own. Indexers find the first hash via the blockchain, use it to fetch the full torrent description via DHT, which in turn allows it to find the torrent via the magnet URL (or alternatively, includes the .torrent file directly, but this trades network efficiency for hosting overhead)

To speed up bootstrapping new indexers, occasionally "rollup" descriptions could be published, which are just torrents that aggregate a large number of descriptions (bucketed say, by date, DHT swarm size, or similar). Add an identifier and public key to these roll-up releases, and you effectively have a trusted "channel" - one guy or group with editorial control over the index they publish, and magically you have something very close to ThePirateBay again.