Nothing really has to be confined to anything. The thing to keep in mind is that anything is possible if you put enough time, effort and money into it. The DLSP doesn't include the property that PPH is currently on, but if Disney really wanted it amended, it could be amended and changed.
The bigger question is whether it is worth the cost, and there the answer is probably no. The idea of building a bridge over a public street for a theme park expansion would be incredibly expensive, potentially unsafe, and just plain unrealistic to achieve. Ultimately whatever space or expansion they could get for DCA over in the Simba lot, wouldn't recoup the extraordinary cost in any reasonable length of time.
So yeah, while it can be a fun little what if exercise, DCA will not expand into the Simba lot.