I personally don't think that PopPops need more calibers than the ones that're already available. They're supposed to be cheap, disposable, one and done kinda weapons that once you're done with, you throw in the trash. They're there to get your ass out of a pinch, and be thrown away when they make the dreaded click, not be remotely effective outside of an emergency piece.
However, we absolutely need versions for the other firearm types. Granted, this is an issue that stems from pistols at large, honestly. They're infinitely more abundant in capacity than any other firearm in the game, and are the only class with disposables. The other gun types need the same kinda love, even if they're functionally identical, but thematically different to the current PopPops that exist.