Anything that can have a bigger blob, like large blog posts, HTML pages (from hostr.cc) documents, encrypted spreadsheets, private lists, long DMs, large zap split setups, group membership events, etc.
We will get into a point that most events will simply be rejected. So yeah, we need to figure out a more accurate way for relays to expose what they support. NIP-11 is nowhere near enough.
For large events, perhaps using HTTPS for resumable downloads could replace WSS requests?
Currently, the issue is storage, which will be the same for http or websockets.
This is an issue with the implementation of the relay. Storing data in a database is not convenient; using files can be an alternative. Although the cost is high, it can be managed through paid services. This should not be a problem.
