The 2-bit-per-transistor ROM using four transistor sizes is wild. Were there other chips from this era experimenting with semi-analog storage, or was the 8087 unusually aggressive here?

Intel also used the 2-bit-per-transistor ROM in the iAPX 432, their unsuccessful "micro-maninframe" chip.

Nowadays, flash uses multiple voltage levels to store four bits per cell (QLC, Quad Level Cell), which is a similar concept.

I wrote a whole blog post about the 2-bit-per-transistor technique, back in 2018: https://www.righto.com/2018/09/two-bits-per-transistor-high-...