Re: Nothing new here
Mainframes ARE servers, much like in the way of any other server - they use the same Von Neumann architecture. Where they differ is in scalability and resiliency (and multiple embedded accelerators, and the different operating systems, etc), but to call them "not a server" is simply incorrect. Even IBM calls them servers (or, to be more modern, both mainframes and Power and called "Systems").
The ability to ship a full machine with resources deactivated and activate using software keys is part of the mainframe for decades. But every other commercial system has been offering a similar capability for ages. IBM I (former AS/400) had this in the 90s. IBM AIX-based systems (pSeries, System p, Power Systems, depending on the year) introduced this capability in early 2000s. HP Superdome had it. I believe even the Sun Fire 15K had it. It is nothig new, has been old news for ages, except that it is news now because Intel wants to do it. It is news for Intel, not for the IT world.
And yes, it works fine, and it is a way to make a server more affordable. And it does not make it more expensive (maybe slightly if you go for full activation, but without the feature, the manufacturers would simply charge the full price on it).
Moreover, these days the HW cost is not the important factor. If Intel charges, say, $2000 to activate a core, Oracle charges $47,000 to license it to run Oracle Enterprise. So, if no all cores are needed, turning them off brings a significant costs savings. This is the major motivation for the capability. The second one is the instant upgrade that it allows, with zero or near zero downtime.
I worked for IBM on technical pre-sales for Power Systems (still work for IBM in another area). I designed many solutions using on demand capabilities on Power Systems, and several large companies use it regularly, along with dynamic relocation of resources, to manage their production systems.