Could this DHT be used to store _any_ content?
But I'd bet you could store information in the DHT itself. Here's the issue: to store the information in the DHT you'd have to attach it to a torrent. To make it relatively persistent the torrent would have to be popular so that it will continue to be seeded and not disappear for a while (like a movie file or a popular music album). If you're doing that you might as well stick the info in the torrent itself instead of hacking it into the DHT. That's what torrents are for.
I suppose you could just keep your personal computer up and keep announcing, but then you are really just storing information on your computer and not really storing it in the DHT. Feel free to correct me if I'm wrong.
Basically it makes it a bit easier to layer your special application on top of the mainline DHT, help your peers find each other, and make it a bit easier to publish some metadata about your peers.
That way you can take advantage of millions of nodes in the DHT and not just the ones running your special application.
But if you need stronger guarantees or availability those should come from your application, not the mainline DHT.
I was thinking more about storing bigger amounts of data, and more cost-effectively. Of course you can't rely on having the data in DHT:s. That could be fixed with incentivization (paying btc for the nodes for storing your data).