Where would this putative slot go? The main PCB is entirely surface mount, and completely full.

Caveat: I'm a software guy. All I can say about hardware is that it magically gets smaller, faster, and cheaper every year, often through custom ASICs and other commercial integrated parts. If we're talking about a box that doesn't ship until 2002, I'd imagine you could recover some space with one of these all-in-one embedded CPU products. Is it far-fetched to imagine the RAM, bus/disk controller, and Ethernet to be on-chip with the CPU? Furthermore, if you were (theoretically) working in conjunction with a major Japanese stereo manufacturer, you'd have access to their parts box, which may include other useful integrated parts, and well as custom-manufactured front panel displays.

Likewise, by 2002, 2.5" laptop hard disks will likely be in the 60-100GB range. If EMPEG went to a single-drive design, you would have room for slots or whatever. Ideally, you'd mount a PCMCIA slot vertically, with front access. I don't think you have room for that in a single-DIN slot, so you either need to find a smaller standard (Sony MemoryStick?), or go horizontal.

Thinking really far out: maybe the car stereo world will standardize on a digital-pre-out and put the D/A's inside the amps. That could cut out the entire analog section of the EMPEG and would help with the ground-loop issues that some folks seem to suffer. A digital standard for in-car stereo distribution could potentially be Ethernet or USB (both are plenty fast enough -- uncompressed CD audio is only 1.5Mbits/sec). At that point, you only have to bridge your in-car network to an external wireless network, placing the antenna in whatever part of your car is far away from other electrical noise.

I'm afraid such additions, fun though they might be, aren't really practicable for anything based even remotely on the current design.

Absolutely. But this is the "wish list" forum, and we are talking about a next generation "MarkIII" box. In terms of small deltas to the current MarkII (would that be a "MarkII+", a "Mark//e" or what?), you're obviously limited in what you can do and the box you built is an amazing thing.