I think it's incredibly unlikely they build a Simpsons land.
First, are they even allowed to as long as Universal has one (they may be; I don't know the details of that rights agreement)? If the property is still a draw, Universal would prefer to keep it. If it's not a draw and Universal gives it up, why would Disney then want to invest in it?
The current viewership is pretty low, even (or maybe especially) among the coveted 18-49 demographic; it's not even close to being one of the highest rated shows on a network. In fact, if it wasn't such a long-running institution, it would likely be cancelled due to low ratings.
It also wouldn't be new, because Universal has already let you visit a slice of Springfield for years. Of course Disney could do even more with it, but why would they want to? Not only for the reasons I've already mentioned, but because they have numerous other properties that would probably have a stronger ROI.