You'll most likely need a custom kernel to root the 5X and 6P.... that's how it is on all existing Nexus devices since 5.0. And considering both are brand, spankin' new devices, it might take a little bit before someone gets someting posted. Once Google posts the kernel sources for either phone, we'll have modified, root-ready kernels fairly quickly.
And if you've gone through the trouble of unlocking your phone, flashing a custom recovery and kernel to even get root access, why bother worrying about any OTAs? You have everything set up to manually flash factory images, which you can do without blowing away user data if need be.