What's a controller? It sounds like some sort of combined battery pack/bluetooth adapter... How much extra desk space does it take? Do you have photos of that?
Also re: battery life, I assume the reason why having a "central" half reduces battery life is the same as the first version. Why can't the computer keep track of modifiers/layers? If you have two keyboards plugged in, you can press shift on one and type on the other and you'll get capital letters.
Is the group buy just for parts or is it for (partially) assembled keyboards? I'm not a DIY eletronics sort, both from an equipment and know-how perspective.