I'd prefer they didn't....(not just because I use both of them, either)
The thing about both Sheik and ZSS, both are light as hell...one mistake against heavier and stronger characters could result in a loss of stock...Sheik can wrack up damage easily, but has limited killing options...while ZSS has one of the most punishable grab whiffs in the game (rivaled only by....herself), which is actually pretty big considering her viability depends on her grab set-ups...Two things I can see them doing for nerfs Sheik: increased KB on ftilt (technically a buff but makes it less spammy) and create a slightly more horizontal launch on ZSS's Up B...literally the only things I'd do tbh...
Anyway...I feel if they buffed certain less viable characters rather than nerfing high level characters it would benefit the meta better...
For example...
...they need help in a bunch of different areas a lot more than others and nerfing Sheik and ZSS (ironically their alternate forms) won't fix their current problems...Samus with her absurdly bad hitboxes and surprisingly limited killing options (such a situational and punishable grab, but no kill throw?)...and Zelda with so many of her best options having outrageous endlag...
When it comes to Link, a couple things that I'd like to see is a slightly increased hitstun (or decreased KB) on his dtilt for some better follow-up options, as well as frame reduction on his nair's start-up to make it a better combo breaker (one of Link's biggest weaknesses is getting tossed around like a rag-doll, giving him a better option to break free would be a valuable asset to his game) also I feel like projectiles that don't stun (ie, Fox's lasers) shouldn't cause hitstun on his shield (mainly because it makes no sense, why would they stun his shield but if they hit his body he doesn't care?), I kinda want his fully charged arrows to have a bit of a shield pierce as well...another thing that makes sense to me since they...well, pierce things...