Have you considered limits with degraded experience? For example you might have a map with real-time-synced pop-up annotations, and someone puts too much stuff

Have you considered limits with degraded experience? For example you might have a map with real-time-synced pop-up annotations, and someone puts too much stuff in there, and things gets too slow. So you add the rule that text over X KB should be hosted elsewhere, and your nice real-time-map only gets a link to it - and that "elsewhere" is much simpler. Maybe it's a wiki page without collaborative editing support. Or as a more extreme version, you have to compose everything on your computer and upload a whole .txt file at once. Something that would be relatively simple for you to implement. This way huge-text users would still be able to work, albeit with more effort... and yet everyone else would be able to enjoy fast experience.