I asked various people about why the KA/KB/MC/XA all used the same die even though they supported vastly different functionality. I couldn't get a solid answer,

I asked various people about why the KA/KB/MC/XA all used the same die even though they supported vastly different functionality. I couldn't get a solid answer, but several people thought that Intel probably used binning (downgrading chips if the more advanced functionality didn't work). The SB was the next version, which used the old die layout with 16-bit bus circuitry wrapped around the outside. There wasn't any Sx version that used memory management or objects, so binning doesn't explain the unnecessary circuitry here. The SB was followed by the SA, which finally threw away the unused circuitry. The layout moved a few functional blocks around, so they did some work, but for the most part the die remained the same. My guess is that chip design was difficult and fairly manual at the time, so it was very hard and time-consuming to make different versions. By the time of the Hx and Jx versions in the mid-1990s, I think layout was much more automated. Looking at the die photos, I don't see structural consistency from one die to the next. It looks like they pushed the button and got something completely different each time.