There was never a concerted effort in the PC ecosystem to force all peripherals and firmware to drop 32-bit compatibility. At some point after a decade or two of x86-64 CPUs, we should have started making GPUs that simply exposed all of their VRAM to be mapped by the host by default, instead of retaining compatibility hacks like only mapping 256MB by default. Resizable BARs should have happened at least a decade earlier, and should have been phased out by now in favor of just always mapping all the VRAM.