Whoa, don't jump to conclusions there. Despite the fact that SMRPG may have been a spinoff of the Mario series, it is still considered to be one of the greatest RPGs, if not games, of all time. The game was simply iconic. It hasn't been mentioned since?!? In case you didn't notice, many gamers have been crying out for years, but never managed to see a true sequel. A second game was planned, but ultimately, the game was cut for Paper Mario. Paper Mario (and its sequels) were all solid RPGs that did very well for Nintendo, but nothing lived up to the pure win of Super Mario RPG. Second, his has appeared since as a cameo in one of the gameboy Mario RPG titles. (think it was Superstar Saga, but don't quote me on that) If you think that Geno has not been mentioned since SMRPG, you are either living in a box or deluding yourself.LOL GENO. He co-stared in one spinoff game that was released 12 years ago and hasn't been mentioned since. What significance does this character have? Popularity, but Toad also has that + has been in every Mario game + playable in multiple more games.
Toad>Bowser Jr>Petey>Waluigi>Rosalina>Daisy>(Every other Mario character)> Every other Nintendo character including Link's uncle>AND THEN Geno.
Second, the game does not possess a true main character. Character development is a heavy component of RPG games. SMRPG was no different. You really got to see a lot of the different characters and use them. Geno was placed on the same level as Princess Peach and Bowser. Geno received as much character development in that game as Toad has throughout the series. The only reason he has not been developed further is because he seems to share some kind of "co-ownership" with Square Enix. It is Nintendo that has held Geno back, not the gaming community.
Geno has more than just popularity on Toad as well. He has a very viable moveset that isn't just a combination of generic kicks and punches. Geno is a star being that has possessed the form of a scarecrow. As such, he has a variety of moves that can be performed due to his "marionette-like" status. He also has the ability to use various forms of magic. Geno is strongly connected to stars, which give him more move opportunity. Furthermore, he possesses the ability to shoot his hands or fire bullets from his arms. Finally, he carries a cape, which has been shown to have several uses in the Mario series.
Almost all of the games Toad has been playable in are sports titles, with the notable exception of a Super Mario Bros. title. His only defined abilities are the ability to pull vegetables out of the ground, swing sporting equipment, and ride a magic carpet. (which isn't so much of an ability, but it is usable as a move) Unfortunately, many of these moves have already appeared, and the basic Toad would end up a lot like a Peach clone. Sure, a moveset could be created from scratch, (like CF) but Geno already has a moveset oozing with potential.
Finally, Geno has the retro thing going for him. He is in a similar position as Pit right now. They were both major stars in their respective titles. (albeit Pit did not share the spotlight with anyone) Both characters appeared a while ago, and have not made a reappearance since. However, fans on both sides are calling for sequels to the games. Finally, Pit has already made an appearance on the virtual console, where new gamers can see the classic game that we grew up on. SMRPG will undoubtedly appear in the VC at some point due to its extreme popularity and classic recognition.