If I'm not mistaken, Zelda is just about the least used character, or she was at least for a while. I remember some tournaments that had 100+ entrants and if two characters weren't used, they were PT and Zelda. A specific one that I can't think of had 150 entrants and every character represented except for Zelda (not even Sheik/Zelda).
I won't deny that she's got it raw in Smash brothers in general because she's a princess without the ability to float, so there's really not much you can do to her to make her extremely good without taking her out of character. However, she's pretty much NeverUsed.
Her metagame growth has been quite terrible, with only three ATs used for her, not even by everyone because of how situational they are... those three being using her momentum after getting launched to use a B move (like transforming and going super far up or w/e), canceling Farore's Wind on an edge for immediate control over her upon reappearance (which would actually make her far better if someone could memorize every single edge and what direction you need to jump, otherwise you kill yourself), and... well, this isn't an AT, but being able to lightning kick certain characters when they trip, which gives her a true combo with the most powerful aerials in the game.
However, even if we were to find out tons of great things about her to counterbalance her severe weaknesses, like being tall + light, being hella slow, having the worst approaches in the game, having THE worst grab game around (yes, worse than ZSS and Ganon and whoever else people like to nane), and amongst other things, she would still be horribly underused. It doesn't matter if they made 20 games of Smash Bros; she will always be a slow princess because that is how she was meant to be, and that's her downfall.
I believe the fact that she was doomed to struggle because of the type of character she is has been long accepted by basically the whole Zelda board. We understand that by playing this character, unless you're a specific Zelda player that we all love, there's really no chance in hell of placing without a secondary, and don't even mention winning. Sheik can help with placing, but that's really about it, unless you're just amazing. This is why we were shocked and overwhelmed with joy in the first tier list thread, when she was listed as upper mid, or just about that. It really brought together the board to think that we had a chance at winning. Of course, we knew she was never really "doomed to mid tier", as it was put. We knew (or at least I think we all knew...) that she was going to hit low tier sooner or later. We also knew that the most important thing was how she did with Sheik, as far as things like tier lists go.
We still love our princess, though. No matter how horrible she is as a character, we still enjoy our pretty hitboxes, our pretty animations, our humorous run, and most importantly, our lightning kicks. I can't imagine anyone there quitting her if she hit bottom tier because we simply love our character that much.
Not sure why I just rambled like hell out of nowhere, but yeah, I can't see her getting any more popular with anything short of a chaingrab. Ah well.