Paid for supercharging, where I live, is still cheaper than petrol. Filling at home is about 1/5 of the price per km compared to an BMW 330i. If I would have to do paid for supercharging it would still be less than half of the price for a petrol km. [1]
Superchargers should still be cheaper than gas. If I recall correctly, Elon stated they weren't looking to make a profit but rather to recoup their investment in Supercharger infrastructure.
That's the biggest downside, from my perspective.