So I got my Nexus 5X 2 days ago and although I have a yellow screen problem (for which I am getting replacement very soon), I am extremely happy to have it!
A habit I have with every Nexus device is to unlock the bootloader and root it on the first day. What worried me here, however, is the recent suspicious information that the QFuse built in the chip "blows up" upon unlocking the bootloader, leaving a permanent, irreversible tamper mark.
Today, upon contacting a Nexus Specialist regarding my yellow screen replacement, I was tempted and finally did ask about this issue. What I got as an answer confirmed my belief and I am sharing it here with you: unlocking the bootloader & blowing the QFuse does NOT void your warranty.
Of course, chat proof is attached to this post.
I hope this motivates everybody here to start using their Nexus devices the way they are meant to be used!
All the best,