In any 'free character' scenario I always see it being tied to something like Nintendo Switch online subscriptions, and the character is an appealing one to try entice more people to buy into it. Because why improve the service when you can just include piecemeal DLC content for random games? We won't give you actual servers to play on but you'll get Geno for free*! Doesn't that make you want to buy a subscription?That'd be great, but why would Nintendo offer another free character? What do they have to gain from that which would be worth more than charging?
*With a paid Nintendo Switch online account. Character is only accessible during your paid subscription. Available to purchase separately at $4.99 USD. Excessive exposure to Nintendo Switch Online may cause premature balding, rashes or death. Nintendo is not responsible for any harm that comes as a result of using Nintendo Switch Online.
Still, the way Sakurai picked a freaking plant for the early purchase bonus makes me think he deliberately wanted to avoid trying to put appealing characters as a free offer, the same way he recommended people NOT buy the Fighter's Pass unless they were absolutely sure they'd want it. He'd rather not pressure people into it. Between that, the difficulty of working with Square Enix and the unlikelihood of another non-Fighter Pass character and Geno doesn't seem to have much of a chance.