Work is continuing, albeit slowly, on the flash cartridge.
The schematics are all-but-complete, according to my colleague. The SRAM for a pseudo 'bitmap' mode has been included as well. I still need to discard a few debug pins on the design as the FPGA pin count has been exceeded on the CHR board, but otherwise it's all good.
I've created the FPGA design, the NIOS, and the software project for programming the flash. The FatFS module for reading from SD card has been compiled-in and it seems the EP3C16 will be adequate for the task (on-chip RAM being the critical resource). The prototypes will be loaded with the EP3C40 in any case.
Layout schedule will depend on the availability and the motivation of my colleague. Assuming he gets bored over the break, we might have something ready for review in January!
In the mean-time, I've acquired a 'sacrificial' (faulty palette but otherwise fully operational) AES console which turned out to be a bit of a Frankenstein. The case is for a 5V model but the motherboard is clearly a 10V design. But I have confirmed it powers up and runs a game.
I also acquired Metal Slug 3 for the MVS, which means I now have episodes 1-3, and I'm eyeing off 4 for a decent price on eBay right now. Of course this is for The Project, and not for playing (or for the sake of collecting). Right!