One reason you would want to buy a Pixel device is developer friendliness. The unlocked version from the Google Playstore is bootloader unlockable which means you will be able to install a custom recovery and flash roms. We normally have to wait a few days for developers to get a custom recovery ready for us. It looks like Dees_Troy already has TWRP booting on the Pixel. It isn't quite ready for public release, but it should be soon!
via @jcase