$5000 is the base price. Fully specced it's north of $13,000. I can't imagine who would consider that a good deal, especially with the release of the new Mac Pro expected early next year.
Those users are likely to be disappointed since Apple did not commit to shipping it in 2018. All they said was that the new Mac Pro would not ship in 2017.
Exactly. Early 2018 is insanely optimistic, since we've heard nothing about it since the pre-announcement. If I had to bet, I'd say 2nd-half 2018 at the absolute earliest.
I think it'll either start at a slightly lower spec or a slightly larger price so not to cannibalize too much of the iMac Pro. I suspect it'd be a dual socket machine, so Xeon W is not an option, leaving E5 or E7 as possibilities.
It'd be awesome if Apple pulled off the technically amazing feat of having a Xeon Phi as the only CPU, but I am not sure it could even be done (and with no virtualization support for it, if it's even desirable). Still would be cool to a level only Apple uses to do.