Two things just learned from the stream; brandon's bad at mario games and that gametrailers trying to make money off merch was previously unsuccessful.
Was that before it had personality though? I don't think slapping a GT logo or Marcus Beers face on something is going to sell.
Bosman t-shirts based on Schluffe, Liquid Bosman or even the bottle of Sprite having a baby with Jet Moto? That's gold. Tabletop Adventures is pretty ripe for some good stuff too.
If I was going to explore if it could be doing now, if probably hold a fan contest to design one, pick a Top 3/5/10 for people to vote on it, then crowd source it so you know if you'll hit a minimum print run for it to be profitable or not.