I'm afraid if we kill SIM cards, the opposite will happen: your phone will be locked to one network, and switching networks means switching hardware (beyond just the sim). I really like that while traveling I can just buy a local sim, put it in my own phone, and use it. That would only work in these wireframes if all operators would agree to support this. Which I think they won't.
Pretty much this. In fact, it's already happening to some extent -- most Verizon phones are sold without a SIM. (At least, not a user-accessible SIM.)
This is likely to shift as V rolls out LTE, which DOES take SIM cards. So we're actually likely to see more intercompatibility as things progress. Except, of course, that everything's still likely to be carrier-locked.