If Pewdiepie decided to play a shmup, he would most likely select the game with the most bullets (probably Futari Ultra or something), insert a credit, then take his hands off the controller and start flailing around while screaming like so:
Only putting his hands back on the controller to continue or shoot a boss that doesn't timeout.
It wouldn't be a showcase of shmups so much as it would be a new excuse for Pewdiepie to ham it up for the camera.
I would assume that most people who watch Pewdiepie don't watch him to see new interesting games, they watch it to either see him playthrough and react to games they already know about, or to watch him react to LOL SO RANDOM meme games.
Since most people wouldn't know about a game like Mushihimesama Futari, between the absurd shower of bullets and Pewdiepie screaming like he's on a bath salt bender they would just assume (yes I would think that most people who are fans of Pewdiepie would be so uninformed as to make this assumption) that these sort of games are just another type of meme game and are not actually meant to be beaten.
I would say that the Game Grumps would probably be a much better option if you had to pick a mainstream gaming channel focusing on humor rather than discussion.
They've played at least 3 gradius games now (Gradius 3 on SNES, Parodius, and Gradius V), and while the commentary is pretty much unfocused stoner dialogue ("Man that boss is shooting out metal cheerios like in metroid!" "Hey you wonder if people ever get General Mills and General Motors confused, and they accidentally order a bunch of metal cheerios for breakfast?") and most of the time isn't even related to the game at hand, the actual gameplay performance in these gradius videos is fairly competent (which is much more than can be said for most of the other game grumps videos), which apparently has to do with Arin being a big fan of Gradius. He also apparently really likes Raiden Fighters (and slightly unrelated, owns a virtual on machine along with a few other candy cabs), but he hasn't played those on the show.
Example:
https://www.youtube.com/watch?v=XJJPJWfBh0E
