(Moves from boxing Little Mac could have that aren't the Villager's boxing light jab include) Lunges, blocking, counter-striking, ropadope, overhand punches, uppercuts, heymakers, slices, multiple jab combos, hard jabs, quick jabs, footwork, in and out (and all about), going in heavy, spacing in, spacing out, body-body-head combos, head-head-body combos, etc. don't exist, along with millenniums of fist fighting history and centuries of boxing history that Little Mac would inherit don't matter.
That's not even me going into styles or approaches, like counter-striker, the classic Mexican wars, standing and banging, defensive fighters, accurate fighters, swinging from the fences, technicality, the classic Rocky "all heart", fighting "big", fighting "small", quickness first, power first, and so on.
Boxing is a deep, technical, and beautiful sport. Fight sports are my favorite sports, and I can tell you, nothing beats a big fight, and nothing tops a high level fighter. It's called "The Sweet Science" for a reason. Add in the arcade-y style of Punch-Out!!, and you got yourself some insane character potential.
(Man I wish I could give you all my boxing knowledge; my uncle, his father, his father, his father, his father, and his father, and perhaps further on were all professional boxers)
Also, the Tekken team is making this. Almost all of their characters are based around a martial art. What makes you think they wouldn't latch on to Little Mac=??? They've made terrific characters out of characters with a lot less to work with, and they've given them all like 100 moves, lol. They could easily get 5 aerials, 4 grab throws, 4 specials, 3 tilts, 3 smash attacks, a A move, a A-A-A (or whatever) combo, a grab move, a grab pummel, a getup attack, and a Final Smash, and have literally a dozen attack options on the table.
Besides, the E3 rumor all but confirms him, and this boxing ring stage proves that point even harder, along with Little Mac's increased popularity. Little Mac was the Assist Trophy most Smash fans agreed should be playable next time around. All of the "Top Grade Nintendo All-Stars" have already been playable in Smash (most of the last bunch in Brawl), sans obviously the Miis, Nintendogs, and K. Rool. It's time for the last of the B-grade Nintendo stars Nintendo stars like Ridley, Little Mac, and Shulk to be playable in Smash.
Everything points to Little Mac being playable. Literally everything.