Well...lets begin with 128mb and see if there will be any use for more later. Maybe there will be an efika mkII.
I think Efika/hollywood will be very useful as A4000/scala replacement. I hope 128mb will be enough for that.
As a musician I can see some oppurtunities as well, as a midisequenser on top of my synthesizer(MOS/hd-rec). Maybe a later version of efika would be onough for sampleplaying and audiorecording as well.

And its good that MOS and Aros gets a common platform. Compile youre software for Aros and run it on your athlon system when you need horsepower.