Er, there isn't a soft-SIM. It is a removable SIM
From the Apple website - "One SIM. Many options.
The new Apple SIM is preinstalled on iPad Air 2 with Wi-Fi + Cellular models. The Apple SIM gives you the flexibility to choose from a variety of short-term plans from select carriers in the U.S. and UK right on your iPad."
OK, so the SIM isn't dead, there is no 'software SIM'. Apple make their own SIM, which is pre-installed, but you can take it out if you want to. Apple have indeed struck deals with many carriers to make it more convenient to switch between operators they support, but you aren't locked in to Apple.
An alternative description is that Apple have become a data-only, global Virtual Network Operator, piggy-backing on partner networks, and they give the SIM away for free because they already have your payment details to charge you for any use. A smart move, but a long way from a monopoly.
Data networks will eventually replace PSTN, because they are actually the same thing with different protocols, but data networks are ultimately more capable and one set of protocols is easier to manage. This is the real story, and a very disruptive one, but a bit less shouty than 'Apple and Google ate my Hampster! by Andrew Orlovski'