A SIM-card is something you can swap and replace in less than 30 seconds, and 100% decouples your device from your cellular provider. The way things should be. It's hardware so it's portable. It's standardized so it's interoperable and works with all equipment, from all vendors.
Why does Apple need to re-invent this?
Why would I want to replace something 1. which works, 2. is industry standard and 3. has proven itself for more than two decades... With something which is 1. not industry-standard but Apple-only and 2. not proven?
What on earth would compel anyone to make such a stupid trade-off? How stupid would you have to be to think this is a good thing?