Preordered one for 1250 USD. I wanted the 5K UP2715K, but I'm not a fan of MST (in other words multiple video cables for a single display), I am also unsure how far this will be a standard with new video card architectures being released next year. Intel Iris Pro and nVidia Pascal. I believe the new Macbook Pro won't be available until April, and by then you may have already paid for the UP3216Q.
The reason I made the purchase, was because I just tried to plug in my U3011 and I really loved the experience of having a single screen with enough estate. Completely forgot how great it is to work with a display with such great colour. Almost pulled the trigger on a P2715Q (45% cheaper), but I believe it is better to have colour accuracy and the big size to reveal details.
4K is already a hard beast to power, and going 5K means having to deal with SLI, which I already have in one of my boxes. Great performance if supported, but also a great set of bugs if the game or application doesn't utilise both cards to full extent or at all. nVidia Pascal looks promising, but I don't expect a revolution.
All pro and premium applications for OS X have fallen behind and along has the need for performance. It's no longer their prime mover. The Chromebook is taking over campuses with their free Office apps and collaborative simplicity. Over 80% of all devices are also Android. The iPhone is great, but the Apple apps are mostly for teens sharing social media content. It doesn't require any power, like it used to be in 2012, when most of the users on FaceBook used desktop/laptops for Internet access.
http://www.macobserver.com/tmo/article/the-new-mac-pro-is-a-failure
is also a good indication that Pro users are starting to look for better packaged deals than what Apple is currently offering. The Apple Pro line ain't dead, but it is surely declining. The focus and the dedication has been moved to products with greater public appeal than the performance wise with longevity in mind. Another problem with Apple Pro products made from 2011 to now, is that they are still strong and will provide professionals adequate power until Intel wakes up again.
Take a look at the last seven years of GeekBench results.