The largest consequence of raising this too high is that cooking markdown can get pretty expensive on enormous documents.
The limit is kind of arbitrary, I do not think anything would explode in fire if you raised it to 200k or 300k in a very controlled environment.
The only clean way to override this line: discourse/config/site_settings.yml at 3610709b6cf859f674a02394f1430bb51f68d117 · discourse/discourse · GitHub is in a custom plugin. The upside is that the plugin is kind of trivial.
I have seen requests once or twice to raise our “max” limit, but it certainly is not a common request.