MacBook Pro mid-2017 High Sierra required to play 4K HVEC files?

Nope. Any computer with Kabylake and OS (OSX, Windoze, Linux) that supports HVEC will do

 

Both Skylake and Kaby Lake work for hardware decode.

"Only Macs with Skylake and Kaby Lake processors support hardware-accelerated encoding and decoding of HEIF and HEVC files at all; this covers all Macs introduced in 2016 and 2017 and 5K iMacs from late 2015. Only the Kaby Lake processors in 2017's Macs support hardware decoding of HEVC videos with 10-bit color, one of the few new features that separated Kaby Lake from Skylake in the first place."

https://arstechnica.com/gadgets/2017/09/macos-10-13-high-sierra-the-ars-technica-review/8/#h1

 

If you're buying now, the only option IMO is Kaby Lake, since it does both 8-bit SDR and 10-bit HDR in hardware. Skylake only does 8-bit. Furthermore, while any machine theoretically can decode 10-bit HDR 4K HEVC in software with High Sierra, none of them are fast enough to do it. Even an iMac Skylake Core i7 6700K chokes on 10-bit 4K HEVC. Stutter, stutter. The Skylake MacBook Pros don't even have a chance for the more complex stuff, even at 100% CPU usage. (Meanwhile, I can do it on my Kaby Lake MacBook Core m3, with under 25% CPU usage.)

Plus Kaby Lake has the hardware for Netflix 4K DRM, should Apple and Netflix ever decide to implement it using this method. Skylake doesn't not have this tech.

 

Yes, Skylake works with hardware decoding for HEVC/H.265 on High Sierra, but only at 8-bit color depths.

The dGPU in the 2016+ 15" MBPs can do 10-bit hardware decoding of HEVC in Windows just fine, but for some reason Apple hasn't seen fit to support this in macOS. Kind of frustrating, but maybe they'll add it later.

 

This statement doesn’t make sends. The code name is for the micro architecture. I suggest you read up.