I would think that this guy's fame would have made this market opportunity super-obvious.
With his own personalized collection of Minecraft toys and all:
Relaively few YouTube gaming celebrities stream due to quality control. Twitch celebrity streamers use YouTube primariy to host stream highlights as Twitch's VODs are not convenient.
Notably, YouTube Gaming, which was YouTube's Twitch competitor, failed miserably since there was no clear advantage to switching from Twitch (among UI/Content ID/monetization issues)
I know many YouTube gaming celebrities who have become successful enough for merchandizing, but not any Twitch celebrities. They're separate markets.
I used Stampy Cat to make the market point, because there were hints that the "alright, let's play this game" spectator video was going to be a big thing, even before Twitch was Twitch.
This guy has been operating since Minecraft was in it's infancy, and he had a large following before Twitch was a big thing.