What is so hard about buying an AK47 to shoot soviet ammo from soviet magazines? Even the more expensive AKs are cheaper than most of these uppers. Add in the price and rarity of (decent sized) hand-crafted AK-upper mags and the annoyance of having to be careful with dirty ammunition because of the jamtastic stoner action, and it quickly becomes an exercise in futility.
Do you see AK47 owners hacking their guns apart to use garand stripper clips or taking a hacksaw to the FAL so it can use Enfield mags? No. Because it would be retarded.
I have already filed this idea with the 40 weaver rails front stock and the ninja sword/flashlight/flare gun/licorice dispenser weaver mount accessories that certain AR15 owners are fond of. Sort of the firearm equivalent of a honda civic with a 30 foot wing, neons and a loud farty muffler.