Whole reason why I wanted one, too many "ifs & questions" for those conversions kits.Get a Kel-Tec Sub-2k and use Glock mags!
I like to pretend and make machine gun noises when I go to the range. Some it's on my couch.The longer barrel of a pistol caliber carbine seldom gives you any significant velocity increase. Here is an example where tripling the barrel length gained 15-fps:
More often than not pistol caliber carbines are purchased so the buyer can pretend he has a submachinegun.
Granted, a 9mm version of the AR can be useful for indoor practice at ranges that cannot or will not accommodate rifles. Otherwise I see little use for something the size of a carbine that shoots pistol ammunition.