Having some crazy thoughts about building a 6 axis machine. I'm thinking of rotation then entire y axis. Will this work? Can any software control such movement in a useful manner?
Yes, you could do this (rotate the entire part around the y axis). This is a common setup for 4 and more axis machining. Mach 3 could control this if your cam software could generate the code. That is usually the tricky part - the cam.