Until June of 2020, on the website predictit.org, one could gamble on the number of tweets that Donald Trump, the whitehouse or POTUS twitter accounts would make over the course of a week. My gut instinct tells me that this was an inefficient market, and that one could fit a distribution to his past tweets and then go from there.
NOTE: this will not work if you get it up and running, but I will leave it up as a reference point.