To me the problem with Geno isn’t that he’s an obscure character (I am a Muddy Mole supporter after all), but rather that he’s an obscure character from a popular franchise. It’d be like putting in Fang the Sniper, he’d just feel out of place alongside the other Mario characters unless they started adding other semi-obscure one-off Mario characters like Tatanga or Vivian - which to be honest I wouldn’t be opposed to, if they revealed Mallow alongside Geno for example that’d be an easier pill to swallow.