Custom chip emulation is quite a difficult thing to impliment as UAE attests to. It is not really up to an operating system to impliment functionality like that just because a few programmers chose not to follow the correct procedures and API's for producing sound in a system legal manner.
Fortunately, most direct hardware hitting programs are games and demos which ignore the OS anyway.
I'd assume any program which used the audio.device properly (and not just to allocate the hardware before hitting the chip directly) would still sound alright under AmigaOS 4.
