Do you think that Teslas made 1 day after battery day will have new batteries? Maybe, but problably not. So there will be onramp for them.
Do you think that there will not be any premium for getting a 'better' battery? Maybe, but would you be willing to "upgrade" for a nominal fee of lets say $10,000 to have a battery that lasts 1 million miles vs current one that is 500k miles? Will your tesla ever even see 500k miles? Thats decades! You arent going to upgrade your car for decades?
IMO 1 million mile battery is good for cars burning 100k miles a year. Ubers, taxis, commuters with 100+ mile commutes one way.
Do you think there will be no downsides to 1 million mile battery over current battery? They are changing chemistry, what if its 1 million mile but capacity is lower? What if capacity is the same, but its heavier, so effciency of the car is lower? What is its charge rate is limited by new chemistry?
I dont know answers to these questions, but just things to think about... there is a good possibility that this battery is just straight up better in all regards. But do you think the upgrade would be free? Maybe? Maybe not. For the entirety of Tesla's existence, they have always had price tiers for different ranges. I dont see why they would give a better battery for the same price. Someone has to pay for the R&D.