Dang, this is why I'm asking now. To see if there is a path forward as battery technologies evolve and pricing improves with technical innovation. Thanks for the detailed response.
Anything at this point is a guess. As no one can predict the future.
If I were to guess though, it would NOT be worth it for you.
First, companies de-incentivize replacing the battery. They make way more money selling a car, than just a battery. And when they sell a battery pack, it means that pack can't go in a car. For this reason, prices are high and inventory is low.
I would be surprised if Ford breaks this trend and makes it cost efficient /convenient to not only replace your battery, but also upgrade to a different battery than what you had originally purchased.
Additionally, even as battery tech improves and prices drop, you aren't likely to see that drop directly reflected in your pricing. Ford knows they can sell a truck for $X. When their costs go down, they don't drop the retail price by the matching amount. They may give you some of the discount, but more often than not, they keep the sticker price the same and maybe add a few extra bells/whistle to make you feel better about paying $X.
This is also ignoring the fact that as battery tech changes, so will other hardware in the car. So the batteries they are putting in F150's in 8 years may very well not even be compatible with other components in your lightning.
If you think you'll want to upgrade the battery, it will in my opinion be a better choice (and cheaper) do so now. As I doubt it will be cheaper in the future, IF it's even possible.