Hmm.. I think we've covered right about everything. And since Little Mac apparently is extremely likely (or pseudo-confirmed) there's just not a lot to talk about until his reveal.
I really really hope too much confidence won't bite us in the rear later. XD
If there were a Punch Out boss, who could the perfect candidate be?
King Hippo:
He'd have a lot of HP to deplete. As it's no stranger to bosses, you probably won't be able to budge him either.
He'll just punch around and ocassionally try to clap you.
Then when his HP is low, he could go "Title Defense" mode where you won't be able to damage him from the front due to his manhole lid. He will learn a new move, the slap+Crush.
Mr.Sandman:
A bit more of a generic boss, but Mr.Sandman could actually put you to sleep with downward punch, and knock your lights out with his Dreamland Express uppercuts.
Bald Bull:
The 2nd most iconic opponent in the franchise, but one that has appeared in practically every game, and even had a spinoff for himself. Bald Bull would attack with his twirly jabs, his devastating hooks, and his signature Bull Rush attack.
Then... Assist Trophies: Should there be one?
Aran Ryan:
I would love to see this crazy guy be all hyper on everyone, to the point it makes players want to stay away from him. He'll run around, stalking the players, offering a handshake, if player hits him while he's holding out his hand, he'll counterattack with a horseshoe.
He'll also whip out his horseshoe in a rope, striking at players from a distance.
And finally, when he leaves, he pulls a Nintendog (from Brawl) and starts making fun of the audience, and threatening them while blocking the screen.
Super Macho Man:
He'll appear on the stage, and will flex his arms and legs while doing poses. The whole stage will go black as a single spotlight will be focusing on him. There will be distracting camera flashes (will have to be toned down to not induce seizures). And if the player tries to get inside the spotlight while Super Macho Man is posing, he'll get mad and perform his signature Spinning Punch which does HEAVY knockback.