Here's the matter with Impa.
She DOES share similarity to

in Skyward Sword, her biggest canon role, as any major Sheikah probably would, with the benefit of some time magic shield properties or something. I still don't quite get what that barrier was made of. Of course, she could be made very distinct in spite of this.


Ninjas can be plenty different.
But, here's the two big things.
1) Inconsistency/Importance -

's always been the hero, with an overall similar design (outside of the games using

's look).

's changed her hair a few times, but stands as the Princess.

, even with his three appearances, stands as the big bad (especially if we count the over half-dozen appearances of his Piggy form as the antagonist), and has the biggest variance in design across his few appearances. Impa is... either a nurse or protector of Zelda. But her looks have jumped across ages and body sizes. Let alone that, Skyward Sword is pretty much her only major role... which the next game bumped her back down to a sage and nanny.
2) Popularity - Outside of Smashboards, I've never really seen her brought up. Of course, this isn't everything. But when someone isn't a major protagonist, main antagonist, or "Princess" level important to their home series as a whole, you either are on par of

as a reocurring second-in-command, uprising established star with strong following

, or just be a Sakurai special "surprise" character

/

.
Impa, just... doesn't strike out in Zelda enough and I just can't see her making a jump to Smash. There's really only one Zelda character that I do and he honestly isn't close.