Pichu isn't an echo fighter.
This next part applies to anybody reading this. There is a bit of confusion as to what separates a normal clone to an echo fighter, so lemme clear that up. As we all know, clones are characters who share nearly all their animations with another character, starting with Luigi in Smash 64, who was a straight up clone of Mario. However, he had differences, such as a higher jump, taller, different properties in some moves, a few different animations, etc. This continued with the Melee clones. Luigi also got further differentiated from Mario, so he became a semi clone instead.
It would make the most sense to think of degrees of cloniness on a scale of sorts. Based on how close the clone's attributes and moveset are to the source character. Like, say, Lucas can be considered a Ness clone, but on a much lesser scale, only sharing forward smash, up air, down tilt, and specials (though they have nearly identical physics).
Then we have Smash 4, which gave us alternate genders for some characters (Wii Fit, Villager, Robin, and Corrin), and also entirely new characters as alts, like Alph, and the Koopalings, who even have their own announcer calls. Are they clones? Nnnnno. They have no gameplay differences whatsoever and aren't considered separate characters, even if they're technically different characters entirely. This brings me to all 3 clones in Smash 4 (Doc Mario, Dank Pit, and Lucina). All of them were originally alt costumes early in the game's development; but when the dev team was chilling after finishing everything else, Sakurai decided, for the hell of it, to give all three slight differences. When they did that, however, they couldn't be alt costumes anymore, as in Sakurai's words, "even the slightest difference in abilities requires a separate slot." Essentially, they couldn't be alts anymore because they weren't exactly the same as their source characters. BUUUUT, they still aren't exactly clones, because typically, clones have much more differences. (Dr Mario is an exception, though; he qualifies as a clone because he has enough differences from Mario).
So, characters like Lucina, Daisy, and Dark Pit, are not clones; they are essentially alt costumes that got promoted. And THAT is an Echo Fighter. Characters that may as well be alts, except for the fact that there is at least a tiny variation for a few moves.
Hope this clears up the confusion between what makes one an echo or a clone/semi-clone. Pichu isn't an echo because his moves have different properties, plus, his hurtbox size is different.
Yeah, I know it would be much more of a hassle (I even stated that in my original post). I think it would be easier because, while yes, spriting would be much harder than copying and editing a model, after that, you're pretty much all done, and you just need to edit a few more moves rather than making entire lines of code like for a unique fighter. (Plus, since they're basically glorified alts, they could feasibly use the sprites of the original character as a base)
Of course, I'm not a professional, I could be talking out of my a**, and I also expect Steven or someone else to come out of the blue and prove me dead wrong.