@Noah
It matters because when he was at his most likely, Sakurai didn't even give him the time of day. And while that would've been a good chance for him to be included, you're right, it wouldn't be the only one. However, he hasn't done anything since then to increase his chances, increase his likelihood, or increase his merit. Sure, the bar does get lower with each iteration of Smash, but from what angle would Sakurai have to be looking to find Vaati the top candidate? Because according to you we should get the second most important and recurring villain next? Then where's Bowser Jr? Potential wise while he offers a unique moveset, so do other Zelda characters. Yes, even Toon Zelda, Tingle, and Impa could offer unique movesets (not saying they will - well Tingle probably would). You seem quick to dismiss popularity, but just because Rosalina didn't have as much as other Mario characters (though she did in Japan) doesn't mean popularity can be dismissed. Sakurai has given it as a reason for inclusion in every game since Melee, and in Melee that's why half the initial batch of newcomers were added in the first place.
And yeah, a character being planned last time can't be dismissed either. Sure it might not pan out, but Sakurai does have a history of implementing characters planned previously, we can't just throw that away because not every single planned character is going to make it in. I'm not saying Toon Zelda will make it in, I'm not saying she's the only or ever best choice, but her role in the series hasn't exactly diminished since she was planned, we can't ignore that possibility. Yeah, she might end up a clone, but despite what people think, getting new semi-clones is still a possibility. We've gotten them in every installment so far.
What does Vaati have above the other candidates? He has potential, so do they. He has relative importance, he has multiple appearances... so do they. Some of them have more importance. Some of them have more appearances. A good handful have more popularity. What exactly would convince Sakurai to add him at this point? Because he's the "second villain"?