Sorry, it seems I misremembered. With the drm renderer enabled, i915.modeset=0 also causes plymouth to fail to show up. With the drm renderer excluded from the initramfs, but without passing i915.modeset=0, splash screen appears correctly.
The net conclusion seems to be the same: the frambuffer renderer works with inteldrmfb, but not with vga16fb.
Sorry, it seems I misremembered. With the drm renderer enabled, i915.modeset=0 also causes plymouth to fail to show up. With the drm renderer excluded from the initramfs, but without passing i915.modeset=0, splash screen appears correctly.
The net conclusion seems to be the same: the frambuffer renderer works with inteldrmfb, but not with vga16fb.