I may be in the minority here, but I really like the idea of the ACA500. The sidecar is bulky, but is a recognised old school way to expand an Amiga 500. If you could make the board in the same shape as the A590, you'd find a whole new market for those units on ebay
Also, I think that it shouldn't be too hard to make an internal version of the ACA500. All you would need to do is make the connector flexible, or at a 270 degree angle. Then you'd be able to mount the PCB inside the A500.
