Honestly I am not an expert on this crap, but I suspect it would be a pretty big rewrite.
ReadyBoost uses a connected device to store files, like a page file, and it works dynamically and is supposed to really work and improve system performance. Also, if M$ could have sold it as a performance booster, or added it to a service pack to improve XP performance, I bet they would have. It isn't like M$ is losing alot of people to other OS'es but it probably would make a few fence riders tip toe into M$'s camp.
Of course, if I understood ReadyBoost completely or OS'es completely I could be of more help, but I work with what I have.
Side note: WTH are the requirements for ReadyBoosy. I have tested my OCZ Rally USB drive, no go, iPod no go (wasn't expecting it to work lol). Oh well, who knows...... well hopefully someone does.