Jack:

First, I noticed that your "wish list" of instructions that aren't part of the 8052 core can be implemented with two or three 8052 instructions. I don't think this is a major flaw in the core. For what it's worth, I've never had a need for the instructions you mentioned. But if I did, I'd just use the two or three instructions rather than looking for a new core.

Second, I think if dozens of semiconductor firms are using the 8052 architecture, it's because it has its merits. And its merits aren't just the instruction set, but also how many people know how to use it, how much support there is for it from third-party tools, costs, etc. Dozens of semiconductor firms aren't going to make the same "mistake," were it truly a mistake. How many firms are making Z80-derivatives? [I honestly don't know, this is not a rhetorical question]

Third, don't hold your breath for a Z80-based MCU from Analog Devices. The market for 8052-based devices is much larger than for Z80-based devices, and Analog has already made the investment in 8052.

Finally, Harvard architecture isn't required by the 8052 core. You can have distinct code/XRAM space, or you can combine them if you wish. Your issue is with Analog Devices, which includes code memory on-chip. In that case, Analog Devices has restricted your options. But that is an Analog limitation, not a limitation of the 8052 core.

Good luck,
Craig Steiner