The problem with this concept is that it can easily go very wrong, as we've seen before. Sheik is in the spotlight only for Zelda to be a glorified assist character. Another big problem with them is that they're simply too different from one another to have true synergy.
No. They're fine together and how they should stay. They just need to do it better. An idea I had is related to the Marvel VS Capcom series. When Zelda transforms to Sheik, they get hit up in the air or away like an explosion. This has cooldown time to prevent it from being powerful. When Sheik transforms to Zelda, they get stunned for a bit in a similar way to Sing. However, again, if overused it gets weaker. This allows them to do both what they do best, while not making one overpowered. I refuse to separate them because the concept was an excellent idea. The execution needed work. Nothing more.
Zelda does need buffs, but she shouldn't be ridiculously good at racking up damage because it ruins the whole point of why she's even in the game. To be a finishing blow character. Sheik's entire reason for being in the game is to rack up damage. That's their literal concept and how they play. This is also why trying to separate them actually ruins the overall character, because it was never meant to be. That's as horrible as making Ice Climber one character total. They're most powerful as a team in concept. It's also why he's at his worst with a lack of Nana, because that was his weakness. Both ideas are perfect in concept, although I'd say Ice Climbers executed it pretty well.
I say just remove the elemental aspect period. It really only applies to a handful of matchups.
Debatable. But yeah, it did get annoying sometimes. I liked the idea, though. As for making us force to switch, I would like that toggable simply for the fact that, yes, people play as all of them instead of one. By doing that, players can easily give themselves the appropriate handicap to know when to switch. Albeit, I'm fine with it gone too, but I didn't mind it either.
Eww, clutch mechanics. I'm sure most Lucario players will tell you there's more to him than the Aura mechanic.
That's the only thing I find that makes him worth playing as, to be honest(for me). Otherwise I'd rather pick Samus or Pikachu at that point. It's a well-designed mechanic, truthfully. I do want it toggable for those who don't prefer it. Actually, if Pichu had that mechanic, he wouldn't such nearly as much.(he'd be pretty cool)
Also, the way I look at it is this; Zelda's overall placement on the Melee List and Shiek's placement on the Brawl list are around where I want them to be separately. Together, they should be a lot higher, like maybe in the A or B tier. Around the top of B.(assuming it goes S, A, B)