As you say, Daedalus, custom chip emulation is petty hard to do and OS4 wouldn't do it at all. Programs that use the audio- och paulaaudio- or whatever.device correctly could be redirected to AHI without much problem, but hardhitting programs wouldn't work.
The Paula-to-AHI patch for AMIthlon is a different business because AMIthlon is more or less a complete emulator. I don't think this could be done so easily on the A1 or OS4 because it's not only the addresses that needs to be captured, which is fairly easy to do with the MMU. The problem is to emulate the precise timing needed to play each sample correctly. Also, harhitting programs usually do strange stuff like tremolo, vibrator, pitch slide etc in realtime on a channel independant of the other channels. This is hard, if not impossible to just re-direct to a soundcard without a complete emulation of the chips and timers themselves as UAE does.
But I'm not sure! Time will tell....