6502 (Apple 1,2,3): 1976
68k (Mac): 1984 (+8 years)
PPC: 1994 (+10 years)
x86: 2006 (+12 years)
ARM: 2020 (+14 years)
If the trend continues, we will see Apple's next architecture in 2036.
That being said, I would really like to see the Mill make it to Silicon - even if it doesn't work in the end, it's much more interesting to me than RISC-V.
I assume RISC-V appeal is because it's open and thus allows people to explore (proprietary) implementations while maintaining compatibility at the ISA level.
If I understand correctly you cannot do this with Mill either.
Their work looks very interesting, but I'm not drawn in writing an fpga implementation or work on a toolchain for it, since I know any success may be impeded by patents