What else can you stuff in the AR platform?

I was just reading about a company that puts the .25 Winchester Super Short Magnum (a .25-06 class cartridge) in the AR-15. Accuracy Systems of Beyers, CO is one such (you have to go near the bottom of the linked page) for a mere $1369.95 for an upper. Of course, this is old news in the AR-15 world but for me, it was a new idea. It would seem to make the home defense/militia carbine a viable deer cartridge (where, like VA, we need to have .23 caliber and greater) with a flatter, more "modern" trajectory than the 7.62x39 or 6.8mm SPC. Not without limitations, it is still thought provoking even for a "Fudd" like myself who hunted the past season with a side-lock muzzleloader and a Winchester 1876 reproduction.  It seems to me to be an infinitely better choice than using of the the AR-10 clones.  Now, on the AR-15 platform, one can shoot from .50 to .17 cal and cartridges to suit most North American hunting situations.