I doubt Tesla will implement a system where you'll get your original battery back when returning after a swap. All of their communication, from the basically unlimited warranty on the battery, to the removal of the "range charge" in the upcoming software is designed to remove consumer concern that they have to treat the battery a special way to get maximum life out of it. I think they see this issue as ultimately limiting to sales and are willing to work around the problem with the swap.
If they don't offer to return the battery to you, then this dramatically simplifies inventory, doesn't it? If it takes five minutes to change a pack and an hour to fully charge, then you only need 12 packs for a lane plus a couple of spares for packs that somehow fail.
I do see this as being implemented primarily in the most remote of locations -- places where you don't want to wait an hour to charge -- between Amarillo and Albuquerque, for example (no offense to the residents of Santa Rosa).
Although I don't see wanting to use swapping often, I know that I would like to to be able to take the Tesla on a destination vacation -- Destin, FL is popular from Dallas, but it's a 700 mile drive -- I know plenty of people who do that in a long day with ICE, so they can maximize their stay in Florida *and* have their own car to drive around. Alternating swapping with Superchargers on the route would be a great way to allow a Tesla to make that journey.