The bad
Apple can potentially dictate which carriers appear on your device as an option for service. If soft SIMs were to roll out across the market then Google or your OEM could theoretically do the same thing. It seems very unlikely that they would be allowed to do this, but it could certainly give OEMs a lot more leverage with the carriers.
As it stands this Apple SIM can be replaced by another regular SIM card, which you’d need to do to get Verizon service, for example, because they haven’t signed up to it. If the future aim is to do away with the SIM card slot altogether, then you’re stuck ordering through the Apple menu system. What if the carrier you want isn’t listed?
What happens to dual SIM users, or people who like to use more than one smartphone? What happens when you want to switch device, sell your old smartphone, and take your number and service contract with you?
We could see the end of smartphone subsidies. If carriers can’t lock you in then they aren’t going to offer the same deals with little or no money down on a new smartphone.