When it comes to audience,I think there is a schism between closed device and external expansion, against open internal expansion. And even that varies within fields and industries.
Thunderbolt is great, don't get me wrong-there are just so many relying on other connectivity options.
As for me, I'm primarily in the market for a machine that can dominate architecture and digital design software. I am looking for serious CPU & GPU performance for both massive 2D and 3D modeling and plans. Prefer most modern connectivity options (again I really love thunderbolt).
I could live happily with a nMP, but not at 2013 prices (*yes there is the storage price drop, but let's be real here) paired with 2013 technology in 2016. Even a table scrap update of thunderbolt 3 and step ups in CPU & GPU would tempt me.
It's really interesting to see all the different fields and how they use the Mac Pro. No one is "right" or "wrong" it all comes down to what works best. For me right now I am limping along with a 2012 rMBP, and serious thunderbolt storage and display-I'd love a dedicated workstation, and keep my portable option too, just can't justify it and still waiting to see where things are at until something comes out, or my current setup is out of commission and then I look at HP Z series.