My old 2009 Mac Pro has had a very long and productive life. The insides of the machine have nothing except one DVD ROM drive from the original packaging. Everything has been upgraded, from the processor to the graphics cards. The machine supports USB type C, and a host of other technologies that were not available when I bought the machine. The firmware has been upgraded to make it seem like a newer version to get a few more years out of the little beast that could.
And this is the reason why I will be buying the new 2019 Mac Pro, the upgradability. The iMac Pro would be fine for me, but it is not upgradable, and I do not want to spend 5599+ Euro every few years for a new computer. I iMac Pro does have a beautiful screen, but I do not need a 5K display. I currently have two 4K monitors hooked up to my Mac Pro, and it does an excellent job. I use my machine mostly for coding, running a few virtual machines, listening to music, as I still use iTunes for my music library, photo editing, watching a movie or two, and once in awhile editing videos.
I do wish Apple did mac a headless Mac Pro with the iMac Pro internals. That would be cheap and give a Pro-Consumer Mac Pro to the public, instead of just having a Business focused Mac Pro. Maybe Apple will evaluate their choices in the future, but I cannot wait any longer. I will be ordering the new Mac Pro when it is available and upgrading the NVME drive to 1 TB. The current base model has only a 256 GB NMVE drive, which is not useful at all.