The hardest part will always be moderation. It will be incredibly difficult to prevent smut and CSAM propagating without people actively monitoring what content is being hosted. But even if you assume random people have the time and are ok with seeing and reporting/filtering out that content, you’ll still never combat advanced cryptographic steganography techniques; a picture of a flower might have content hidden inside it somehow that encodes the bad content in a way that you’ll never find it. On top of that, moderation is work that no one wants to do for random content they don’t care about, but without people hosting content they don’t care about, links will die too quickly to be useful. Imagine if you posted an image to a niche community, and then had to keep your system on for hours, days, or weeks, ready to seed it to the one lurker who happens across it, and then maybe they also seed it.
tl;dr it’s a very difficult problem…but honestly maybe AI breakthroughs can help with it