It is not limiting the hardware whatsoever, there's clearly a misunderstanding of what this is.
The thing is an actual, physical Nano SIM card. It has nothing to do with the hardware or software. When you get an Air/Mini 2, you can open it up and immediately pop the Apple SIM out and put in any other SIM card. You can also get another Apple SIM to replace the one that comes inside it. You can lock the Apple SIM to AT&T, and immediately remove it and put a T-Mobile SIM inside. The device is not locked. It's a programmable SIM card, that gets made static.