That'd be cool, but mega-bucks, as you imply.
I have seen "Hard drive switches" that are touted to be just the thing...3 drives hook to a switch, you could mark them: Net, Open, Free, then push which you want to boot today.
OTOH, you'd have to have more than one switch (or more than one box) for Linux: RH, Suse, Debian, Slack, Mandrake, Gentoo,
Alphalinux, ALT, ART, ASP, Astaro, Basic, Beehive, BBC, BRD, Byzantine, CAEN, ChainSaw (vroom!), ClarkConnect, Cool, Core, etc., etc., etc.,
Gee, so many....I'd think we need an entire boxen farm...takes forever just to load a list on my 56K modem... 😉