I honestly don't know what such a diagram looks like for a modern processor
Some processors (like the Motorola 68xx series) also use "prebytes". ...This avoids making the opcode map huge with special codes for EACH operation
The same bits might be there, but they're scattered throughout the instruction (presumably in ways that make the hardware smaller and more efficient...
Or not, with microcode I think it can be totally random.
Re the lower-level explanations......something that shouldn't be left out of the discussion - which is rather important - is the role of the clock, and timing diagrams.