Battery swapping for fuel is of limited importance as a Tesla strategy.
The battery not being integral to the car is important for the long term. The point of a car battery should be maximum utility to achieve the highest economic value. Most Tesla EV batteries will decline as much from age as from use. Currently, in the early stage of EV, Tesla is making a major effort to minimize battery anxiety. (Battery anxiety is the mostly subconscious cousin of range anxiety).
In the future, Tesla may:
1) Lease batteries: The maximum use of the battery is in the lease term, and the terms are enforced by software. Most Tesla battery lessors would be able to use the battery additionally for home energy storage or grid services. Tesla Energy will sell distributed grid services, paying participating Tesla EV owners.
2) Rent Batteries: Like lease, but month by month. Trade up or down for a fee.
3) Rent for a trip: Like battery swap today, but with a big battery option. Probably a daily fee to encourage prompt returns.
It is a bit nuts to spend $40K on a battery and have little idea of the actual yearly cost. Tesla is positioning itself to address this major EV adoption issue with a removable battery. It works out great that Cali. pays for part of the effort.
With EV adoption, the U.S. alone will have more than a trillion dollars worth of batteries on wheels. Maximizing the economic benefit and utility of that enormous societal investment is a big deal.