Would you consider for example Deluxe Paint OS friendly? How does P96 deal with HAM8 for example? It is really that kind of software that I am thinking of, they are very much OS friendly, yet rely on the chipset.
PS - it is almost scary to see you answer on my long list of issues without really disagreeing with any of them! 
AFAIK (and been told) HAM8 is AGA only, a600 is ECS, so what are you talking about ??