I must confess that Little Mac not being in this game could turn out to be a dealbreaker for me.
I simply cannot picture this game, with a boxing ring, without Little Mac.
Honestly, what purpose would it serve? A flat platform? There's final destination. A flat platform where you won't fall into an abyss? We got Bridge of Elding (pre-explosion), or they could just use the old SSE stadium without abysses... Why a BOXING ring? Not a Dojo, not a wrestling ring, not even the Pokemon Stadium knockoff of SSE's stadium.
Unless it's sort of a new Sakurai-trend where he'll try to better represent multiple characters throughout a single stage, therefore (smash logo, and) characters with a similar arena can be represented without having to think up too many.
And secondly... there's also the fact that, so far, it's a Wii U stage. Punch Out was released on the Wii, not the 3/DS, therefore it makes sense to have it represented on the Wii U.
I don't think I'm making anything up when I say he's a popular Nintendo icon (yet severely unrepresented). Heck, he's always in the first line of Virtual Console releases! Along with Super Mario Bros and Legend of Zelda! There's honestly, not a better time for his inclusion.
And I'm sure the lack of WVBA logo means something. We'll just have to wait to know what.