I think the original idea for mounting the MG-4 was to allow ammo commonality with the individual soldier weapon so they can live off the same pool. Seems kind of stupid, really. There should be enough place to store a few hundred rounds of extra 5,56 for the dismounts and have 1.000+ rounds of 7,62 for the coax. Which would then be strong enough to knock down a mud wall at least.
Because again, the original idea of using the main gun for anything the 5,56 can't do seems a little short sighted, as that would really stress the precious 30mm stock.
A .50 coax is a nice idea I think, heavy enough to properly suppress and knock down stuff, without having to resort to the main weapon. But going from 7,62 to 12,7 would probably really eat into the storage capacity.
I wonder if a remote .50 (or 40mm GMG) could be added to the side of the turret in place of the Spike ATGM system when that is not needed. Would also do pretty well I imagine.