alt Hacker NewsAlso, I raised the question at https://retrocomputing.stackexchange.com/q/30743/3722 and one of the answers points out the 1984 Rockwell R65C29 Dual CMOS Microprocessor. It was two standard 6502 on the same die using the same bus to access the same memory... and of course IBM mainframes did it decades before.
If we're going that direction, National Semiconductor had a 2 'core' COPS4 processor in 1981[1]. I have some in a tube somewhere (unused).
[1] https://www.cpushack.com/2014/08/25/national-semiconductor-c...