What you are describing is called accelerated virtualisation, except that your version is unco-operative. If you make it co-operative then you will have proper virtualisation.They'd launch as a program, then sieze control of the CPU (unco-operative multitasking), and make Mac Toolbox / System calls as required for display, IO, etc.
Also I don't see why, if uClinux can run the Macintosh Plus hardware, why we can't just boot it from a floppy or hard drive like we do with *NIX on our other 68k Macs.