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@jecel over on retrocomputing forum has just posted a writeup of his 8 bit CPU design - and associated computer design - which he put together in response to a challenge on G+ back in 2013.

It's an 8 bit machine, 12 registers, relatively regular but not CISC, and the kicker is that addresses are 24 bits (and the registers come in sets of 3)

See here:
Retro8 - what would have been the ultimate 8 bit micro?

It's a squeeze, but Jecel has assigned a 40 pin pinout too - and also a 28 pin pinout!

That is an interesting machine, but where are the load and store instructions?

It's a cunning plan: most opcodes take 4 bits to specify the 'register', which gives 12 codes for the one-byte registers, and 4 codes for indirection through the 4 triple-size clusters. Another format uses 2 bits to specify the 4 triplets.