Given that Google itself is the manufacturer of Pixel devices, I wouldn't hold my breath on them allowing you to keep this ability forever

Two of my deGoogled Android phones were Pixels (4a and 7a) and one was a Nexus (6p). I know them well, though I never ran Graphene on them.

Pretty sure I read Google was no longer going to publish device tree sources for Pixel phones, which will make ROM development for them significantly harder, whether or not the bootloader is open.