But the grandparent poster didn't name many technologies, they singled out the bitcoin blockchain specifically. A technology that through the popularity of its function has made it a popular target to have other things bolted onto. But popularity of the blockchain hammer does not turn all problems into nails.
You don't need any of that if you just want a torrent index. There's no need for consensus and no need to keep a secure record of the past. Bitcoin needs to prevent Joe from forging messages like, "Bob sent Joe one thousand bitcoins," but there's no corresponding scenario for torrents.
There are some projects that try to search directly from it :
https://btdigg.org/ http://btindex.org/ https://github.com/laomayi/simDHT
That said, I'm not quite sure why this needs a blockchain... A URI is either in the system or not in the system... Why would one need a consensus algorithm to store URLs?
Blockchains are about consensus, not storage...
I guess a Git repo would do just fine. It just needs to be regularly updated and signed-off by TPB's people.