If it works in the A500, chances are it'll also work in the A2000, and that is of far more use to me (tho I own both). In the interest of cost effectiveness, 32MB of SDRAM is plenty. Dual channel IDE would be awesome. No need for CF, since there are plenty of CF2IDE adapters out there. Ethernet is a nice idea, but USB would be better.
Now what would REALLY kick @$$ would be a PCI bus on the accellerator... Then use a cable connected between the accellerator and a "PCI dummy" card to plug into a PCI backplane mounted either internally (on say an A2k) or externally in a PCI expansion tower (A500/600).
Of course you'd have to buffer the connection at both ends, and shield the hell out of the cable... I think this would be WAY faster than any current PCI solution since it'd be connected directly to the local bus of the accellerator.