But, currently, selecting Google Asurada in Kconfig (`make menuconfig`), display initialization cannot be disabled, and I do not see a way to disable USB init either.
That's a fair point, I think that's just not implemented because nobody needed it yet. Display init is already globally guarded by the display_init_required() function in src/lib/bootmode.c, so if anyone wants to add a Kconfig in there that's easy to do. (Maybe it can be tied to the NO_GFX_INIT option if we untangle how that interacts with MAINBOARD_FORCE_NATIVE_VGA_INIT a bit.)
For USB, I think usually it just doesn't take any notable amount of time so nobody has bothered to make it optional yet. But that could certainly be done too if there was sufficient interest.