Hmmm...
First of all, I don't see any reason why only the CPU would be able to "look" at other characters, items, or events. Nothing about the direction of a character's head influences gameplay significantly. Therefore I propose it's just something that every character - player or CPU - will divert their attention to specific things for a more interesting/dynamic/interactive-looking appearance, just like Link does in The Wind Waker and Twilight Princess.
Second, I'm going out on a limb making this guess, but I wouldn't be surprised if what Mario is doing is actually a new kind of jump. Sakurai's stated he wants to improve the air game. What if you could do a "smash jump." That's not to say it's an attack, but more like a boost in any direction. You basically smash the analogue stick in any direction and instead of hitting the A or B button to get a move, you hit the jump button to "boost" in that direction. Like a dash, but faster, possibly omnidirectional, gains a set amount of distance, uses a jump, and has a small delay/lag/cooldown period afterward. Right now, when people jump it matters little what direction they hold or push the analogue stick in, so all jumps can be seen as from the neutral position. Of course holding a direction during the jump will influence its direction, but smashing won't do anything special. Imagine using one of these jumps to directly intercept someone in the air instead of jumping and leisurely making your way to them.
I know that proposal has little evidence, but it seems like something Sakurai would do, and a natural progression of the game's controls.