Google is replacing some Nexus 6P RMAs with the Pixel XL according to users on Reddit. There are some unknowns in this scenario for the time being. It isn't clear how long Google may be offering the Pixel XL as an alternative option for those that had submitted an RMA for their Nexus 6P, so with that being said anyone who hasn't already done an RMA with Google for the Nexus 6P battery shutdown problem, now would be the time to do so as you get a newer, better phone in the process, and there's no telling if Google will stop sending these out and go back to replacement Nexus 6P devices again.
All that said there is at least one caveat. This only seems to be for anyone who purchased their Nexus 6P from the Google Store. The phone was available through other retailers, so if you didn't buy the phone straight from Google then you won't be offered a Pixel XL as a replacement. According to the Reddit post it doesn't matter if you're out of warranty or not, so if you have been having this issue and you bought from Google you should still be ok and get the help from Google that you need.
The Reddit post mentions that it isn't guaranteed every single Nexus 6P RMA will get a Pixel XL instead of another Nexus 6P, so anyone with one of these phones still shouldn't go into an RMA submission expecting to get one of Google's latest phones, though it is probably very likely. It's also being suggested that the Pixel XL units that are going out are new and not refurbished units, at least for most people, so this should be even more incentive for anyone who still uses a Nexus 6P, or at least still has one they bought from Google, to submit an RMA. While it hasn't been verified where all of the locations are that Google is sending Pixel XL devices as replacements, there have been reports of consumers in the U.S., the UK, and in Canada getting them, so you'll want to double check even if you aren't in one of these countries. Again, it's unclear how long Google will be offering new phones to consumers who had the Nexus 6P with this issue, so anyone who has the device should jump on this quickly.