Eh, new question, if only one of them had to make it, who would you choose, K. Rool or Ridley.
K. Rool, because I feel he'd fit my personal playstyle preference the best, and that, if he's not in this game, he won't be in a new one for a while because Retro sucks at inserting any semblance of meaningful personality into their DKC games. That, and objectively, he's wanted on a more global basis (having been the world's most wanted Nintendo newcomer for years now), hails from a larger, more prominent series, and wouldn't be "pretty impossible" to develop. I say this with utmost respect to Ridley, my second most wanted character.
Against Little Mac? "He's popular, but maybe not popular enough in Japan! You know, despite Sakurai calling him a 'legend' and granting him AT status before his reboot was even a thing." Or perhaps, "He'd have a boring playstyle! Nevermind that Wii Fit Trainer's entire schtick is being a generic balanced character who happens to be shocking, a Star Punch mechanic with Doc Louis potentially coaching from the background would be dull."