Nostr is something like IPFS but not based on a filesystem mapping, instead it's an account/post/comment event distrtibution network, where IPFS is a... well... filesystem.

If it doesn't cost routing fees to send Sphinx messages it's a good thing it's not popular.

If it does cost fees to route messages, then all we need is more people to run sphinx capable LN nodes and they can spend the sats they earn and cost goes to near zero. The network benefits from a lack of spam, due to the economics of its pay to play game system mechanics.

If you could get paid to relay people's messages, why stop at instant messages, why not have long form and forums as well.

One of the goals of Indra is to do exactly this, not only anonymising but also monetising content delivery, and with mechanisms like prisms, to pay content creators and content hosters from the service access fees.