You have to think of the logistics of it. Potter only works because it's at the back of both lands, just creating a seamless ride between parks without disrupting the parks themselves with the attraction. Beyond that, where would this attraction lead to? Jurassic doesn't have a presence in USF and there isn't a large abundance of space available for the taking anymore with Fallen, F&F, Nintendo all set for future replacements/expansions to the park, all taking of expansion plots or the most viable replacements.
I'm all for expanding Jurassic as much as the next person, but expanding to USF seems like to much of a stretch, especially when they have the TL land that could potentially be chopped into (or re-purposing existing areas).