If you're timed out, show timeout timer in the input box, preferably next to the label of current character count.
This could also include a slowmode timer.
Insperation for timer (Progressbar also cool)

Would be interesting how this could look when hiding input box. Personally I think it might be cool to just have a progress bar then at the bottom of the chat.
This issue is out of scope of the Chatterino project.