Some benefits, but weary of Apple's grand plans
From a telco perspective - this could reduce cost through lower SIM distribution costs and a reduction in box breaking (ie a handset is sold with a SIM included, handset gets shipped overseas, SIM goes in the bin).
From a users perspective, assuming all networks were made available greater selection could result in improved price transparency and greater competition as lesser known mobile operators like giffgaff.com would be able to be included in the list. Also as InITForTheMoney mentioned perhaps some protection if the device is lost/stolen.
Regarding roaming/ switching to get best deals - it will be interesting to see their plans to tackle number portability. However if the plans to have porting within 2 hours comes into play, it might not be such a hassle to switch?
It would certainly change the 'affiliate'/ SIM distributors business models.
I'm on the fence - can see the benefits for the consumer, but equally I'm weary - surely Apple has their eye on revenue share options.