At the end of the day, the worst that could happen is that bumbledumbs leave agreeing with him and thinking he presented his case fairly/reasonably. This slop is more of an irritation than anything of consequence.
Shovel Knight is a great game (with great music) but it is just that: a single 1-year old game, an IP not owned by Nintendo, relatively niche (700K across all platforms), and currently unreleased in Japan. At the moment, there is every reason to doubt the rumor that he will be included in Smash Brothers. Third party characters have been held to a very high standard. Shovel Knight is an interesting game, but the series and titular character do not even come close to the heels of Pac Man, Snake, Ryu, Mega Man, and Sonic in terms of impact and recognition. To tout him as an "indie" rep is to attach his name to projects that have nothing to do with him whatsoever. I do not see the character being included, even with the rumor attached to him. If he is, I would be very underwhelmed.
King K. Rool is an old character and it's true he hasn't appeared in any main game since 1999. Despite this, K. Rool remains beloved. He beats Shovel Knight in virtually every poll taken in the community. Moreover, his games -- unlike Shovel Knight's -- are internationally known. This is true even among casual audiences.
While the Mii costume might raise the possibility that K. Rool might not be included as a full fighter, this possibility is currently uncertain: there is no evidence that the ballot had anything to do with K. Rool or any other character's mii costume. None of the other Mii costume characters have been highly demanded as DLC characters besides Inkling (an obvious promotional move). If anything, the Chrom and Heihachi costumes suggest the importance of the pre-ballot phases: both were considered for the vanilla game. If the consolation prize argument were stronger, we would be seeing other ballot-popular characters as Mii costumes as well (there are only limited DLC slots after all). But we have not -- K. Rool is the only one, besides Inkling.
I struggle to see why Sakurai would pick a low-impact third party character with a game that has not even been released in his region rather than a Nintendo newcomer from a multi-million selling series that is popular all over the world.