I've had a MK12ish build for some time now, and although I do enjoy it I'd almost certainly have gone a different path and achieved at least equivalent and likely better performance as a result. Mine runs a NF 2.5-10 and a Centurion Arms MK12 barrel. It's accurate and does everything I've asked of it, but it's heavy for what it is, and gives up a lot up close for not much top end gain (If any).

I think the MK12 concept has, as others have said, been outshined by 14.5"-16" Midlength guns with LPVO's and decent barrels. There are quite a few manufactures today making chrome lined barrels that will run alongside most of the stainless offerings out there accuracy wise. If I was to do it over again, I'd likely start with something like an LMT MRP with the monolithic rifle length MLOK receiver and pair it with a 16" barrel (probably chrome lined, but maybe a proof CF barrel for the weight savings). You'd have no issues with bipod loading causing POI shifts, and rail mounted lasers would have no issue holding zero. Throw a 1-10 Razor HD in a 1.5" or 1.7" mount and piggyback an RMR/ACRO on top and rule the world.