Everybody is annoyed at how long it takes computers to boot. Some use hibernate mode to save a copy of the system in a booted state, which is one approach. Booting procedures have also gotten better about running stuff in parallel.
How about watching a system as it boots, and noting what disk blocks are read to boot it. Then save that map for the disk defragmenter or other disk organizer and have it try to rearrange the files needed at boot so they are all contiguous
and close together. This should reduce the role of I/O as a boot bottleneck. Many disks today can read 50 megabytes in a second, and most OSs only need to access a few 100MB in order to boot, and they have the ram to only need to read files once.