I'd like a full size/full scale M1A in .22lr
Or
A 10/22 style take-down in 9mm or .45acp that takes Glock mags.
That's basically what the new Ruger PC Carbine is....a takedown 9mm with a threaded barrel, that uses Ruger or Glock mags. It has interchangeable mag wells. It would be awesome in a 10mm and 45acp.