All relays already have size limits. That shouldn't be any problem. We already transmit NIP-95 and other very heavy binary events, like GiftWraps and NIP-04 DMs as well as 2000+ key follow lists, text files, blogs, spreadsheets and wikifreedia entries (5-10Kb for a good article). Relays and clients can reject on the size and that's their choice. But big events will always be there.
On the formatting, we just don't have the flexibility on the parser to decide what to parse per event kind. We just use one for everything. So, if people use markdown or ascii doc, like fiatjaf is requesting, we will have just one parser/renderer for all these types.