I too was captivated by thoughts of modularity, but ultimately decided that I would rather down the coin for a new device rather than upgrade. That and the constant delays led me to cancel my batch one pre-order.
I was really close to buying just as they were "released" but other things caught my eye and now I'm thankful I didn't.
The modularity thing sounded great in theory but then I thought again about the concept. Their aren't many things more modular than a modern PC. I built the one I'm using now about 2 or 3 years ago. It has an Intel 1155 socket for the CPU and since then there have been 1150, 1151, and I think one other format. Any upgrades at this time would involve a new motherboard.
Yes,the CPU socket is modular and an easy swap, but that doesn't mean you can get much use out of it.
evolv or Yihi wouldn't have any obligation to CM; either would design the best board they could even if that meant changing the physical size. Look at the difference between the DNA40 and the DNA200. I don't think there are any DNA40 mods that would contain the current board.