It it was completely up to Universal, they wouldn't. But Nintendo also has a say in decisions relating to their properties. If SNW or Pokemon was to go into KZ, it wouldn't be a problem. But to have two of Nintendo's major properties (and the two most recognizable by far) in a brand new park, then one in a prebuilt park? That could potentially be a problem for Nintendo.
Plus, I don't see Nintendo taking up more than 30 acres at maximum. The new park is rumored to be over 100 acres at least.