Or, will we need to wait until the "new" modular line you are working on is released? If it's a waiting game, are you able to share any idea of timing?
The M4 is far down the list at this time. There are other modular things we are working on but M4 is not one of them. I hesitate to say any more about the new stuff because it is not reality just yet.
Never picked up either one, just had an M4.
If they're looking at going with a modular head or combo in the near(er) future than considering rackmount, I'd definitely vote for four modules, if possible.