People bringing up Ridley, K Rool, Banjo, and Terry to Geno don't seem to understand what mode the former's merits. Ridley is a recurring antagonist in a tentpole Nintendo franchise that only just got in because Sakurai finally figured out how to make him work as a fighter, K Rool was also a recurring antagonist though he stopped being used in more recent games, Banjo Kazooie were massive titles back in the N64 era. That's not getting into how all these characters were much more popular and more requested than Geno ever was.
Then there's Terry who yeah on his own isn't the biggest character but is the most prolific and popular character from SNK's lineup that even before Smash were putting him in everything. Nintendo wanted an SNK character and Terry Bogard is their main boy. It's basically a pecking order. Which goes into why Cloud, Hero, and Sephiroth all got in before Geno. He's just much lower on the totem of characters they could get from Square and even in the future there's probably still other characters Nintendo would likely be interested in choosing like more FF characters, 2B, and Lara Croft.
If he ever happens then a lot of stars are either gonna need to align or Nintendo would finally be scraping the bottom of the barrel after getting most notable characters in Smash