This is a little late, but I DID write it up so here we go:
At the risk of incurring the ire of Sheik mains (although a lot of Sheik mains actually agree she actually does need at least one nerf) I actually am extremely worried about a future where the balance adjustments have ended and absolutely nothing has been done to tone down Sheik's abilities to a more acceptable form.
I know it's been mentioned a few times but regardless of my track record against Sheik, and keeping in mind that she'll never be as dominant as Brawl MK, I really do not want to see another Smash game turn into one where everyone flocks to the best character and that's the end of the metagame. I know she's not the easiest character in the game to pick up, but I can say with certainty that she is easy enough such that a large proportion of people who just want nothing more than to win can just pick her and start seeing results relatively quickly.
I don't 100% agree with the notion of buffing characters to Sheik level, ala PM, either. Because as you might recall, when PMDT tried to bring characters up to Fox's level, we got 3.0 Mewtwo and Lucas, and they were COMPLETELY bananas. There's a certain level of ability that characters can be pulled up to before things start getting stupid, and in Smash 4's case, that line is drawn somewhere around where ZSS is, NOT where Sheik is. If you try to cross that line with too many characters, you get results like PM 3.0, and no one wants that.
And... since I brought up the topic, I would like to point out the potential competitive merit of Smash 4 with a nerfed version of Sheik, or just with Sheik not existing at all. With ZSS as the best character in the game, a much more dynamic metagame has the potential to exist, as the "best" character in this format has design weaknesses (poor grab, lousy UpB recovery, has troubles against low crouchers and charge projectiles...), and actually loses matchups, to my understanding. Even if they're minute, the things that work against ZSS in this game would allow more and more characters to shine, as you'd start to see characters who counter ZSS become prevalent, or even characters who counter those ZSS counters! There's a lot of potential to be had in a game like this, and I do find it, actually, REALLY ANNOYING that there's a single character holding back that potential, even if it's not to that great of an extent of what MK did to Brawl.