The dilemma to me is that they have every theme that I can imagine covered. Magic Kingdom, Epcot, and Animal Kingdom cover fairytales, the future, adventure, animals, the world, traveling, and much more. Hollywood Studios fits every movie, or at least it does nowadays. To me, the only idea for a fifth gate that makes some sense is a villains themed park, but a villains themed area makes more sense as a land or mega land for me.
Besides coming up with an idea for an entire new gate, they have the issue of the expense to build up all of the infrastructure for the 5th gate, as well as staffing for the new gate. Building new lands and attractions seems to generate as about much demand as a new gate containing that land would, and these lands can be appended on to existing parks without the already mentioned costs of infrastructure and various other expenses.
In the current state, it makes no sense to build a 5th gate. There just does not yet seem to be an idea that wouldn’t fit in an existing park, nor a reason to spend the money to build a new gate. However, I do think that a 5th gate, however implausible it seems today, may be built in the future.
I’ll add this in as another curve to the question before I finish my post. As of now it seems that we are all considering a new gate in a very limited sense. Universal considers Volcano Bay a gate/park, and I do believe that Typhoon Lagoon or Blizzard Beach may one day be rebuilt or replaced by a new waterpark, which would be a new gate but obviously not the 5th gate that is often mentioned.
So there we go, my extended rambling on this question. To me, a 5th gate is awfully far fetched today, but may be plausible in the future. The costs associated with a new gate, as well as an abundance of areas to expand upon of their existing parks, push me away from seeing a 5th gate as a possibility anywhere in the near future. With that being said, I do think a 5th gate could happen eventually, but that would be a long ways down the road.
