Two interconnected moments in history with the popularity of microcode in microprocessors need to be distinguished:
Firstly, the ratio of price, volume and speed of various types of memory;
Secondly, the ratio of manual labor and the development of automation, including the theory of compilers.
The heyday of the microcode came at a time when the means for ...
For those interested in the hands-on use of microcode, including how to implement a CPU (1802 - which was NOT microcoded, but a FSM control unit) and a display controller, I developed a compiler that generates the [horizontal] microcode and instruction mapper memory. https://hackaday.io/project/172073-microcoding-for-fpgas
As I understand it, later chips like the 8086 and 68000 use microcode
of the conventional ROM variety.
This is simply not true. 68000 CPU used a combination of PLA-driven decoding and ROM-driven microcode engine. Look https://dl.acm.org/doi/10.1145/1014198.804299 for reference (remember that there is Sci-Hub at your service if you know DOI: https://sci-hub....
But it's not a ROM; [...] it's actually a PLA
Then again, a ROM and a PLA is essentially the same technology. What differs here is not only the decoding, but that in case of the 6502 only the decoding part is present and it's not monotone.
Such compression is obviously useful. Die space is expensive
True. But it's worth to note that the cited answer says &...
The Amiga 1000 era VRAM chips had 4-bit data pins and 4-bit serial pins. I think this is shown in the A2024 patent. On the patent, they keep them D0-D3 but I think it's easy to imagine eight chips arranged as 4x2 where the 4 wide make a 16-bit bus and the two tall make two serial busses that are muxed with BLANK and the pixel clock (28MHz on Ranger?).