Does a low resolution desktop capture of someone slowly and sloppily typing messages for the viewer into notepad count as text-based?
How about a gigantic compressed image of mostly plain text attached to a post that requires an account to download files? Maybe also with a colored/patterned background to make trying to print the monstrosity even more fun.
Or maybe actual embedded text, but served via 300 MB of bloated libraries and fonts and a script that disables right-clicking and text selecting.