Knowing how similar the Saiyans and Humans are biologically, would it not be feasible to have another similar species that Saiyans can cross-breed with? Has there already been such a thing, and if so, how powerful is it?
As far as I know there hasnt been shown any other similar species that saiyans can cross breed BUT, there might be in the future since Vegeta's brother has a girlfriend named Gure from another species, who doesnt even look very human alike, and I suppose that if he chose her as a partner it's because they can have offsprings. Gure is a short, alien with black eyes and two nostril, horizontal egg shaped head and a white skin color that might have a very low tint of green or grey. He appeared with her in a non canon special, but he was mentioned later in canon movies like Battle of God and Broly, so he became canon. Though we dont know if his girlfriend became canon with this too.