Why waste the concept of the Ministry of Magic on a D ticket attraction, when you can build the whole damn thing, ala Diagon Alley, and create a fully fledged out-London area... While leaving room for additional expansion.
Can Lightning Strike 3 times?
Also, I'm on team "Doing this would be borderline too much Potter". I just noticed a few things that push me towards this speculation.
Yeah, I'm kinda feeling this is a possibility for the 3rd gate. Do a combined MoM and FB area down there. Kills two birds with one stone. It gets FB into the parks and Potter(with wands and Butterbeer) into the 3rd gate. It mitigates some of the "too much Potter" talk as it would be in another park as well. Probably won't happen, but theres enough of a reason there that I can see it.