Why stop at Quadruple booting? Get AMIX installed, and then throw a bridgeboard and Emplant card in there! :-P
That would have been one killer machine to own in the early 90s...
As for the multiple Kickstarts, I've never had much luck softkicking anything other than 2.04 from the HD or 1.3/2.04 from SuperKickstart. I have a spare set of 3.1 ROMs, but it's much more fun to get it softkicked. :-)
Once the Kickstart image is loaded into memory, though, you can do whatever you want to the Devs:Kickstart file. So your script could rename the current one to Kickstart.2.04, rename Kickstart.1.3 to Kickstart, and then launch the cold reboot.
It might make more sense to put the 1.3 image on a WB_1.3 partition - cleaner version separation, too.
I guess there'd be no avoiding the early boot menu, then...
Might a softkicker like SKick be easier? It has a GUI...
EDIT:
AMIX clears the kickstart from memory... maybe you could do a small dummy install that boots a core environment and then reboots?