As popular as the XDM lineup has been, I don't understand why they didn't design shorter mags/grips for their "compacts". They could shave 25% off the capacity and still be around 10rd (45acp), 12rd (40sw), and 15rd (9mm)...which would be more than ample capacity in each case. In fact, that's a typical round count for most full framed guns in those calibers.
They don't need a subcompact, but a true compact XDM would be nice. I've got an XDM45, and I really enjoy it. If they were to make a true compact version (3.8" with reduced capacity), I'd buy a 9 or a 45 and make a carry gun out of it. But until that happens I don't any myself having any use for the 3.8.