I don't think there are any devices where "withing a few seconds" is a useful target for the startup sequence. Most devices should really be instant, which means hibernation / full memory snapshots and your real boot system becomes mostly irrelevent. Everything else is really in "meh" territory. That said, OpenRC is already quite fast and both my laptop and desktop boot in a few seconds using it - the EFI takes much longer to do whatever it does and hand control off to the kernel than it takes from kernel to desktop login screen.