Apple should make a brand new Thunderbolt display 24-inch for brand new Mac Pro and brand new Mac mini.
Tricky - part of the point of the Mac Mini is that you can use a cheap/existing display with it. Meanwhile, the pro graphics/video people that go for the Mac Pro are going to have diverse requirements vis. size, resolution, screen finish, colour calibration, hoods, usability with other hardware etc.
The strong point of the Thunderbolt display was always as an extension screen and docking station/charger for a laptop.
All-in-one like iMac is a waste and anti-ecological because computers may last for about seven years, but displays last more than 20 years.
That's been true in the past, but I'm not sure it holds at the moment.
Certainly, current 5k displays are a kludge, effectively acting as two displays, each with its own DisplayPort 1.2 connection (AFAIK, even the new TB3 display does this - its just that you can run two "virtual" DisplayPort connections over a single TB3 cable). DisplayPort 1.3/1.4 and whatever the next gen HDMI is are needed for true 5k support - but uptake of those is slow (I think because Nvidia, AMD and Intel are all playing not-invented-here) - and TB3 can't support it. Your TB3-only 5k display might work fine with with your 2016/17 Mac, but don't count on it working with new computers 3 years down the line.
Both Intel and the USB consortium would like either TB3 or USB-C alt mode (confusingly different) to be the new display standard - but with both technologies already a couple of years old, you can count the number of USB-C displays on the fingers of one hand, and the number of TB3 displays on the fingers of a boxing glove. Partly because the vast majority of TB3 and USB-C ports out there will only output video from Intel integrated graphics or low-power mobile dGPUs. The discrete PCIe graphics cards preferred by power users simply don't have USB-C or TB3 ports - adding a dGPU-driven TB3 port to a PC is a kludgy affair involving a TB3 adapter card with an
external DisplayPort cable looping round to the graphics card. Bletch.
...so its really not clear what the future standard for display connections is going to be. However, the one thing you
can be sure of is that hell will freeze over before any Apple-made (or Apple-by-proxy like the LG) display comes with more than one input (count your lucky stars that its not a captive cable) - so they will
never be an option if you expect your display to work with your
next computer.
Meanwhile, with only 2 5k displays on the market (HP & LG - the Dell is discontinued) and no fully non-MST 5k-capable external interface that might still be relevant in 5 years - the iMac is probably your best bet if you really want a 5k desktop.
If you don't want 5k (and its overkill for anything less than 27"), then there's plenty of choice of 4k/UHD displays, which are easier to connect.
