If I had the money, or the skills to do it myself I would have:
1. A carbine with interchangeable barrels in 9MMP, 38 Super-9MM Magnum ?, using 1911 magazines.
2. A carbine with interchangeable barrels in 40 S&W and 10MM Auto, 1911 magazines.
3. A carbine with interchangeable barrels in 45 ACP...