> what does this mean for users who want a completely FOSS stack for their phone (let's ignore the baseband for now)?

And also ignore locked bootloaders, DRM code in ARM TrustZone, never updated BSP that make most devices use old kernels, userspace blobs for graphics and video playback, lack of proper hardware documentation and fact that most of out-of-tree drivers that are open source are simply horrible.

Google never wanted FOSS stack on your phone in first place. Same true for phone manufacturer's, hardware vendors, carriers, media companies and governments.

So there simple not much you can do other that support rare open hardware efforts and use extremely overpriced custom-built phones.