You use relevancy, which is not an issue nor is it a criteria to Sakurai. Which means that it won't cause a single thing to happen.
Sunshine did not exist during Melee. So it couldn't have been repped. Sakurai wanted to give that game some reference since it deserved it too. So he did that in Brawl. In SSB4, he'll either rep the two Galaxy games, or if other mainstream Mario titles come out, the latest ones. Galaxy was released probably too late before Mario's moves were decided. Likewise, Sunshine is very underrated, so giving it some loves, which could be because Sakurai might like the game for all we know, is not out of the realm of possibility.
We don't know what logic he follows in this. We do know that relevancy is not a factor whatsoever, which you just proved right there. If relevancy was a factor, we'd have no FLUDD. Latest game means nothing, except he might take from it. He might or might not take from Skyward Sword.
I'm saying you shouldn't specifically depend on it for your reasoning, not that it won't be used. You don't know if it will be either, after all.
Getting back to Zelda herself. Unless Sheik gets her own slot, we don't see the Down B gone. In fact, there's little reason to. Sure, giving Sheik a Deku Nut is easy. But Zelda? They had enough trouble giving her a moveset as is.
