The battery decay is going to be gradual, even though noticeable in a Model S, given its huge battery, it would still be a drivable vehicle even if it loses 50% of the battery capacity. So that 14-20K expenditure will not kick in till 15 years or so with a patient owner, which is pretty much lifetime of many cars in US.

And in 15 years the batteries will inevitably be much less expensive than they are today.

And hopefully much more powerful, extending THAT purchase even further.

I wouldn't count on getting much more kWh into lithium. But the batteries probably will degrade slower in the future.