I have to admit, a 30 cal ( 300 blackout ) MV would be very interesting, and It could lead to having all 3 in the series of modern rifles in 30 cal when the magnum arrives.
But in all honesty, I'd most likely stick to the 223 simply for ammunition availability.
I think sticking to a single caliber makes sense from a business point of view, as 90 percent or more would elect to use 223 and othercalibers may create headaches that aren't worth the time.