"Drivers who choose to swap must reclaim their original battery on their return trip or pay the difference in cost for the new pack."
That seems... inconvenient.
I envisioned it as an insurance-like system: you pay for battery swaps, which cost X amount, which goes toward the collective maintenance of all the batteries in the whole system. Thus you don't have to worry about which battery is yours, or the health of your battery, or anything about the battery anymore. That simplicity alone makes it worth the price of admission.
If they're worried about specific batteries and specific costs and specific maintenance tied to you, then I think they system has too many complex details to make it an easy snap decision. UX won't be as good, not as smooth, and it'll deter people from using the service... I think they need to go the collective route to make this work.
It should be like battery insurance: you'd just never have to worry about it, and there would be an extremely smart system ensuring the health of every Tesla battery on the road. "Should" being the key word here... but maybe that's the plan, hard to say.
(Are the Model S batteries even that cheap?)