The Zelda series always sells well, but it's definitely a tier below Mario and Pokemon in terms of both sales and popularity. While it's popular with gamers, I think they'd need to be careful making an attraction so that it can appeal to Nintendo fans and people who may have never played a Zelda game. That's why I think it needs to be a LC replacement - it'd fill the same niche for people who've never even heard of the series, but it'd give video game fans a HUGE draw to go to IOA and the attractions would be big upgrades from the junk we have now.
Also, if a Zelda expansion doesn't have a ride with a massive, terrifying Guardian animatronic that follows around the ride vehicle (similar to that dinosaur that chases after you in Dinosaur at DAK), than what's the point?