so I haven't been following any of the 3rd park rumors, and there are like 230 pages in this thread. What is the rumored consensus on a possible groundbreaking, and what exactly would be the theme?
It's complicated: let's just say that first things first, the land situation needs to be cleared up. Right now there's an ongoing lawsuit between Stan Thomas who owns parcels around the Universal-owned land, and he owns UCPM III which holds the master declarant rights for all the properties. If you look at this map, you'll be able to see which party owns which land:
Universal Resort Expansion?
Today, there was a scheduled mediation between Stan Thomas and Universal as for the ongoing lawsuit over whether Universal can build a park on the land. Most likely, the lawsuit is Stan Thomas' way of forcing Universal to buy him out of UCPM III at a high price (since most of the UCPM III land is only going to be useful in Universal's hands).
If there's a settlement reached soon based on today's mediation, then that would go a long way towards clearing up at least the legal issues.
But there's other issues as well; for decades in the 60s-80s, Lockheed did a lot of missile testing on this land, and that cleanup started around 2004, but I don't believe it ever finished. So there's still possibly toxic cleanup that needs to be finished before anything can actually be built. And there's the matter of rearranging various things like the bodies of water on the land.
Once you get past all of that, you can start thinking about building another resort. But it'll most likely take at least 5 or 6 years from now for the "first phase" of the next resort to be completed. All we know is that the first phase is like to be the next dry park + a larger CityWalk + at least 2-3 hotels + a transportation hub. Those are the most obvious things that need to be completed around the same time. 2023 still seems like the best guess for opening based on what we know.
As for themes, it's really up in the air, all we know is that Universal's been trying to get Tolkien rights and possibly Star Trek rights. There's a lot of guesses that one of Nintendo's IPs will be held for the next park as well (possibly Zelda if it doesn't appear in the US before the next park). And there's always a possibility for Fantastic Beasts to add a Harry Potter element to the next park. Jurassic World is a possibility but that might just go to IoA and replace Jurassic Park if they choose that route.