I currently have no idea how much effort I will put in other than "some".
My art (not remotely representative of my t shirt designs) is here: https://scyy.fi/art
and previous t shirt designs I've made are here: https://www.redbubble.com/people/scyfer/shop
People are also trading
Update: I have put in 2 hours of work in (and don't know how much additional effort I will put in other than "at least an hour").
Related market with different probabilities: https://manifold.markets/rachel/who-will-win-the-manifest-merch-des-2e56430eb54b sweet sweet arbitrage
crossposting a comment I made on the other market (per market poster's instructions):
I don't have anything finalized right now, so instead of posting a particular design here, I'll post a link to a tumblr page that'll get updated whenever I have a new favorite contender(s): https://refgal.tumblr.com/post/747336154281590784