Hi,
This would be an awkward setup if you ask me, but who knows! Depending on what you want, it could become something unique. I suppose it would work. But it’s weird to have 3 mixer sections in one setup. Unless you want to do dedicated Stems stuff or something.
Although the 4a and the Micro are called CMD as well, I’m quite sure the modular idea of expansion is more about all the other controllers in the line, cause the 4a and micro are kind of ‘all in one’ already. But, you can break the rules right 😉
Most logical idea:
Start with a MM-1. 4 ch mixer and the only one with a USB hub (4 ports)
Expand to a max of 4 others in a combination as wished; for example
2 PL-1’s, one DC-1 and one LC-1 added would give
A 4 ch mixer + a left platter/deck + a right platter/deck + 2 hot cue/samples/fx control etc dedicated units.
Maybe your idea would work for you though. I suppose it would work (not sure) and I suppose a lot of midi mapping would be involved…