FWIW, the MCGA chips have been decapped and imaged:

https://siliconpr0n.org/map/ibm/72x8300/mz_mit20x/ - 72X8300
https://siliconpr0n.org/map/ibm/72x8205/mz_mit20x/ - 72X8205 (partial: top metal layers accidentally got removed)
https://siliconpr0n.org/map/inmos/imsg171a/mz_mit20x/ - IMSG171A RAMDAC

VileR wrote on 2020-10-05, 18:44:

For now I've been looking a little deeper into that Model 30-286 (VGA, not MCGA) video BIOS. Mainly to satisfy my own curiosity about whether those character bitmaps at E000:8F00 onwards are ever used at all. I can't find any code with an obvious reference to that data, at least nothing as obvious as the references to the well-documented 8x8/14/16-line charsets. So these mystery-meat bitmaps may just be filler left there by a programmer who was feeling artistic.... although that feeling was not necessarily justifiable. 😉

Bumping this because now we have an answer: https://int10h.org/blog/2022/06/ibm-ps2-30-28 … dden-vga-fonts/. Thanks to Tom from ardent-tool.com for helping to piece it together.

So there *was* a use for these fonts after all - they just didn't really think it all the way through, so it all falls apart with later BIOS revisions. Not the kind of blunder you'd expect from IBM, but I guess this is what they call a "teachable moment". 😀