Why would you want a HD in there? A SDHC card is future proof and by the time you release will probably be bigger than any HD you could propose today. I think Minimig already utilises that.
Look at those NDS mod cards, which are expandable via MicroSD card. They are so awesome. I wish there was an Amiga in there instead though. If only you could fit an FPGA on the expansion slot, or something that would accellerate emulation significantly enough for an NDS to emulate an A500 adequately. Of course the screen has a lower resolution, but perhaps you could compress or crop the image to size.
Hey, I would consider destroying my NDS to put Amiga emulation internals in there.
