OS4 has improved memory management and knows about virtual memory
You could have virtual memory on AmigaOS 3 already... remember VMM or GigaMem? Nevertheless, you are limited to 4GB shared address space still.
and as far as I know it now knows about proper threads as well
Nope. There is pthreads port/implementation but CreateNewProcTags() in OS4 DOS is almost identical to AmigaOS 3 implementation. To make it work current implementation needs lot of changes.
It may not amount to much, but it still is an improvement over OS3 where you can only add these things by breaking a lot of unwritten rules.
True. However real value is in better and faster hardware. Compiling complex stuff is bit different on slow 68060 than on PPC.
But fundamental limitations are still there... you cant implement proper fork() without ditching current 68k and PPC programs, and it might be still impossible...
