BEFORE YOU SHOOT ME, HEAR ME OUT!
Yes I'm aware there has been an over-saturation of first person shooters on the market, but Mario + Rabbids: Kingdom Battle showed us that Mario characters with guns doesn't have to be a bad thing.
Also, one of the most beloved games by Nintendo (mostly Rare, but still) in the 90s was GoldenEye.
Someone even did a GoldenEye mod that incorporates Mario character models into the game, and the overall reaction has been quite positive so far:
This got me thinking that, provided it uses more cartoonish weapons like Mario + Rabbids did, a Mario FPS could work. Obviously other aspects would have to be considered, such as making the violence much more pretend and silly (enemies disappearing in little puffs of smoke, sent flying into the air from regular shots, etc.), and adding in more traditional Mario elements like platforming and coin collecting.
Well, those are my thoughts on the idea, so provided we keep it a civil discussion, let me hear your thoughts. :)