How often do you adjust the brightness of your screen that it becomes a requirement of the monitor purchase? I ask because you're severely limiting the options with that requirement.
For example, I have a 34" LG 5K/2K Ultrawide display with the resolution set at 5120x2160, it has a 450 brightness, offers Thunderbolt connection, as well as HDMI, Display Port and two USB ports, has passthrough power to run a 16" MacBook Pro, and cost me the same as the much more limited Ultrafine.
True, the 27" Ultrafine sold on Apple's website has a webcam built in, but you already have it on your laptop. It also has a higher PPI, but only a bit more (I really loved the pixel density of the 27" Ultrafine for sharp text, but I honestly don't notice that much of a difference).
The number one thing about the Ultrawide is that with the 5120x2160 resolution, I can actually use that resolution – unlike the Ultrafine, where it's virtually impossible to use the 5120x2880 resolution because everything on the screen is too tiny.
The downside to the Ultrawide I have is that you cannot adjust the brightness or volume with the keyboard. The built-in speakers suck in comparison to the MacBook Pro's speakers (but then again, so do the speakers in the 27" Ultrafine), and the Pixel density isn't quite as high as the 27" Ultrafine (but as I said earlier, I don't notice that much of a difference), and the brightness is only 450 compared to Apple's MacBook display and the 27" Ultrafine's 500 brightness–and while I can notice the difference, it's only slight.
I should comment that I work as a graphic designer, so these specs are important to me, but perhaps not to others. Bright display, crisp clear text at small sizes are very important to me, and so is the resolution because it means I can have many panels open along with my actual documents and still have the document view at nearly 100%. If those things don't mean anything to someone, then they really shouldn't be looking to spend this kind of money on a display.
As for Apple displays, don't bother waiting – you more than likely aren't going to get anything from Apple in this size/price range anyway.
[update: I should have started out by saying that I used to own the 27" Ultrafine - I purchased it with the 16" MBPro when they were first released. The display died just a week ago (not even 3 years old). I suppose I could have sent it in for warranty repairs, but I can't go a month without an external monitor waiting for LG to repair it – I would lose more income with the lost productivity than the cost of the new monitor)]
