I would expect more, so that cores don't get memory starved. The M1 has 4 fast cores and 4 slow ones. If we imagine an M2 with 8 fast cores, I would expect it to need 16 channels to have the same performance. That's a lot.
Dunno, the M1 CPU package is tiny, thin, power efficient, etc. It's got 4 memory chips inside the package. I don't see any particular reason why a slightly larger package could have 4 memory chips on one side, and 4 chips on the other to double the memory bandwidth and memory size.
However the M1 is already pretty large (16B transistors), upgrading to 8 fast cores is going to significantly increase that. Maybe they will just go to a dual CPU configuration which would double the cores, memory bandwidth, and total ram.
So yes, at the very least 8 DDR4 channels, or one per core, but I'd expect more from a workstation-class board.
Now, speaking of the board, all those memory channels will be funny.