They can add more if they manage say 15% increase in cell energy density and the rest from the pack. The 2170 iirc is around 250Wh/kg while industry best is 300Wh/kg and in a recent intereview the CEO said something very important, they plan to phase out cell in modules and modules in a pack scheme and just make the entire pack one module and the top lid of thr pack will be the floor of the car itself. Realistically speaking they should be able to make a 100 kWh pack at the same weight of just under 500kg with well established technology. It’s also been 3 years since tthe Model 3 launched, it’s time for a capacity upgrade. The competition like the Mach E and Polestar 2 will bring around 100 kWh packs in the same price point as well. Last but not least bother the Model S and Model X will get more capacity by the end of the year with the Plaid drivetrain making space for the cheaper models to get more range as well. While right now they don’t have to increase the capacity they will have to eventually and Tesla has so far chosen to stay abead and be the first to increase range even when thru had no competition. The charging speed (more time spent at peak power) and lifetime of the battery should also increase not to mention more power to make the cars faster. There is no downside to making longer range versions, it will maintain Tesla halo image.