The question is though, could you get away with a 20000 character post?
If it was spam, you might get banned for some short amount of time. If it was meaningful, everyone would be an ass and just go "tldr" at it. Pointless either way.
What does tldr mean?
too long didn't read
Some megathreads have gone over that character count, thats why people put [Reserved] for the first post, so they can go on in that other post.
20,000