I totally wanted this a bit ago, but couldn't justify it.
It just costs too much in relation to a Threadripper box, and doesn't have the same performance. For 5k you get... 4 cores, and while SMT4 is neat, it's not going to make up for, as an example, the 32 cores a 7970X (which ends up building out at about the same price) has.
It's kinda only useful if you're willing to spend a huge amount of money for okay but nothing special performance, need the more open platform aspect, or are doing POWER development.
If it was half the cost, it'd be twice as appealing, but, well, it's not.
That was more of a personal story than an analytical assessment of more open vs closed platforms.
I'd say, though, that the person that doesn't care about performance AND doesn't care about price is the rare person, and that the current pricing (which, I'm entirely sure is being driven by having to be in bed with IBM to do this at all) puts it out of the realm of essentially anyone who might be interested that doesn't have a very compelling reason to need a POWER-based system.