The 810 was a huge concern for me. I mean, all of last year I was extremely critical of it, but threw caution to the wind and preordered it anyway. Still shocked with how well it's performing. I mean, it's a beast and all those overheating articles/comments we all read in 2015 doesn't apply to this version. No clue if Google, Huawei or Qualcomm (or a combination) is responsible for the modifications, but whatever they did is certainly working.
Oh, I was also just as concerned when I heard the larger Nexus was going 810. Based on the disaster that was the GFlex 2 on launch, I was worried...
OK... get ready for one of my patented (somewhat) long-winded monologues....
It is most likely a combination of all parties. Qualcomm giving guidance about kernel configuration and thermal management, and Huawei and Google working together to make sure that the phone is properly set up. Keep in mind that this is a big phone, a big phone made of an excellent thermal conductor at that (and stuffed with a lot of thermal paste). So the phone not only sheds heat quickly, what heat it does generate is dissapated over a large portion of the chassis, leading to lower temperatures. I mean, I had a G3 and that had the SD 801, which was the least thermally throttled SoCs in recent years (i.e. even when it did throttle, it was only slightly so and it'd hold that until the Sun burned through its fuel). But even with that, that sucker would start to get hot right near the camera housing (remember that placement, I think it's LG's thing)
Look at this post:
A look at the One M9, S6 edge, LG G4, and Droid Turbo through the Flir One
A S6 (Exynos 7420), G4 (SD 808), M9 (SD810) and Droid Turbo (SD805). They put them under an FLIR cam and started cranking away on them. The S6 was the hottest of the group, in the sense that it had a spot on the chassis that recorded the highest local temp (120F to the side of the camera), but the rest of the chassis was the coolest of the four to the touch. The G4 had similar results, albeit a lower temperature (114). The M9 (112) and DT (110) had lower temperatures, but the heat was equally distributed throughout the entire chassis.... which makes perfect sense as the materials in the DT and M9 are thermally conductive, whereas the G4 (plastic) and S6E (glass) are more insulators.
(Yes, I know the M9's kernel management was an absolute mess) If you picked up all four phones, which one would you think is coolest/hottest? I am guessing most people would probably feel the cooler bottom section (where we most often hold our phones) of the G4 and tap that, with the hottest of the bunch, the S6E, as the next 'coolest'. And since the M9 and DT were warm all over... they'd probably come last.
To the 6P. Another website popped the 6P under a FLIR camera and ran a similar test. The 6P never got higher than around 104F just under the camera... with a good portion of the lower chassis in the 80's. That's a good 16F lower than the S6E (wish they had a Note 5 FLIR test somewhere).
So.... in conclusion (there was much rejoicing.. .yeaa).... the 810's thermal issues, at least when they pertain to the Nexus 6P, shouldn't concern anyone in the least.