I personally would not be surprised if KIA does not offer an upgraded battery or if the cost of the battery would be the same as replacing it today, around $13,000. The traditional model of automakers and dealerships is to Sell New Cars, for that they bring out new designs, added features and improve performance that encourage people to purchasing new cars. This might change, I really hope so.
The main reason I would be interested in a Tesla after the lease of my KIA is over is because, if I am correct, how Elon Musk is changing the dynamic of automakers/customer and allowing updates direct to the car, possible upgrades to battery when future technology is available and not looking to just sell new cars (again I hope) although this could change as well.
3.5 years is a long time and much could change before then, time remaining on my current lease. Much can change.