The new iMac Pro strikes me more as an act of desperation, attempting to assuage the Pro users by releasing something to make them believe Apple cares about the Pro market.
Mind you, the iMac Pro is impressive engineering, assembling some serious performance in a (date I say it) thin package – setting itself apart in a Space Grey package.
I have no doubt that a lot of the engineering that went into iMac Pro, we will see at the end of 2018 in the redesigned (allegedly flexible and modular) new Mac Pro – hence iMac Pro is a good harbinger of things to come.
Starting at $4,000 for the entry-level model, I have no doubt the top-configured model will ring in at *very expensive* levels (probably above $8,500) – and you have to wait until December for availability.
Aside from RAM it offers no expandability or means to upgrade it.