A report from Pike's Universum (via 9to5Mac) claims that the upcoming iMac Pro will feature Intel’s next-generation server-grade Skylake-EX and Skylake-EP Xeon processors, which are a whole lot more powerful than the Core-X chips initially expected.
The tech blog says that the information comes from firmware files contained in the macOS High Sierra developer beta, which refer to Intel's LGA3647 socket, not the desktop-class LGA2066.
Another bit of information mentions the presence of a MacBook Pro-like ARM coprocessor, which Apple's laptop uses to power the new TouchBar. It is only speculation at this point, but this could mean that Apple may be thinking about bringing Touch ID to the iMac Pro.
A server-like CPU (and the addition of a second processor) may seem like overkill, but Apple did say that this would be "the most powerful Mac ever made." And, at $5,000 (£3,928) as the starting price, it should be.
The keyword there, however, is "starting price:" ZDNet recently calculated that a maxed out iMac Pro could in fact cost something in the neighborhood of $17,000 (£13,353) . At that price, a server grade processor could even start to make sense.
The iMac Pro will launch this December, and come with up to an 18-core Xeon CPU, Radeon Vega Pro graphics, 4TB of SSD storage, and a maximum of 128GB of ECC RAM.