As someone else said; a low-spec and a high-spec 4000 box. No "wedge" 1200, ever.
I'd have done the low-spec 4000 with on-board Zorro slots (no riser) and a couple of ISA slots (as an a2000), with a fixed CPU. I'd have pushed for the 8mb Chip RAM but fixed it at 2 on the low spec machine. 28mhz 030, 2mb RAM (in a pair of 1mb SIMMs) as standard on the motherboard. Maybe a CPU slot (as per the A3000 and A4000 as it was) - dunno.
The high-spec machine would've been much like it was, excepting:
A 2nd video slot, occupied by the AGA display chipset. Future video cards could have gone there, thus "upgrading" at least the video chipset. As soon as the PCI spec hit, (1993, just a year afterward) I'd have opened the riser/daughter board specs and allowed (if not created outright) a PCI riser card and moved away from Zorro. Rather like the DCE G-Rex did, I'd have had a cable for "local bus" attachment to the (PowerPC) CPU card to ensure maximum speed.
Assuming this fictional C= survived, and the 4000 hadn't been outright replaced, I'd later have released a PPC card around '95 or so (whenever Apple made the transition) and ported the OS whole-hog to that.
That'd be the last AGA machine update. After that, new systems altogether - probably farm out chip design to 3dfx (remember, we're now into the early late 1990s - '96 or thereabouts) for video, embrace GLide or OpenGL, etc. etc. I'd also be investigating migration to Intel architecture, but now we're wandering far afield...
