Disney will concentrate their focus on current parks. Even when Universal opens a third park it wont have the huge effect many seem to think. Sure they can put a park together fast just like they build attractions fast. Outside of a couple of things the rest are formula screen attractions that only differ because of theme. Its not original. I like some stuff at their parks for what they are and enjoy going to ride specific things a few times a year, but on the whole, it still lacks Disneys creativity and feel of parks, even when Disney just throws something together. Im glad it takes Dis longer to do things and I dont mind. If they max out the expansion areas and really put money into the 4 parks they have, Universal isnt even close to Disney in terms of offerings. The gap will widen over time and Universal will be a step above other "theme" parks but nowhere close to Disney. Im of the mindset FIX what they have, max out the parks already there using the infrastructure they have, Do it WELL, and watch the repercussions it has on universal.
Any new true theme park is going to draw a massive crowd for a while. Just on the basis of being new. If Universal dumps the $5B+ into a new park to build something worth having, people will be all over it for 5 years. The problem becomes what happens after 5 years. Building something new is fun and exciting, maintaining it is expensive, necessary, drudgery. See EPCOT and Disney Studios, 1990-2015.
I think Universal was on to something with their "when your vacations grow up" campaign. Not that true Disney fans believe, or that I believe myself, but many, many people think Disney is for toddlers through tweens while Universal is for tweens through becoming parents. If Universal builds another park, which seems incredibly likely, they have to play to this theme. Because there are simply too many parks in Orlando already for an American vacation. You really don't want people to split vacations, you want to capture the whole vacation.
Universal's best chance to do that is to be a highly themed coaster and thrill park. There isn't another Harry Potter out there right now to grab kids from Disney. So don't try. Do what you advertise. Don't be screens and simulators. Be thrills and spills and PG13 type rides, shows, restaurants.
As a coach, I tell people all the time that when you are facing the biggest, baddest team in the league, you can't beat them by doing what they do. You have to find a way around them. Disney's refusal to build true thrills and spills coasters, something I have no problem with, is also a competitive weakness. Take advantage of it and do something Disney doesn't. Don't try and out Disney Disney. It's not going to work.