IPFS and Nostr are both brilliant but they have their limitations. The main issue I see for an app like seedling is that by submitting your content you lose control over it. You cannot edit or delete.

Ideally many different hosting options should be supported.

You could create a Nostr protocol with a delete message, but the problem there is of course it would be a "soft delete", since anyone scanning the messages under the hood can see the original. In some sense a regular site is like that (you could see it on Internet Archive, but maybe that is less likely to be done, and it is coming from a secondary source anyway).