I think 2 reasonable issues in the future will be:

1- Economic incentives for storage in relays (specially images and videos), eventually several relays will be paid (though cheaply, still an entry barrier)

2- Spamming and widely considered undesirable content being sent. (Platforms and local apps might need to create some basic AI for enhancing UX)

But I do think both of those issues are able to be reasonably solved 😉