Sorry to disappoint but that's not a Video port.
As I'm sure everyone has realised by now this IS an RGB video port. I'm pretty sure that the designed meant it to be a VGA connector but put the wrong component on his schematic (15-pin D vs 15-pin DSub)
is there any way to replace the RTC card into the WSI for some kind of hand-made RAM-IDE card?
Should be very possible. All it would would require is someone with a CD32WSi to debug the pinout of the 184-pin connector using a Multimeter and a bit of sense. Once that is done the schematics and logic for a 68000 to DRAM interface is very simple and can be done using even some of the smallest PLDs.
I don't think it could be commercialised because we've no idea how many of these devices were ever produced.