The Tesla Model S currently has a 400-mile range, so this would represent an incremental improvement.

Personally, I can't see driving that distance without a break (at a supercharger) somewhere in the middle, so the incremental range benefit is definitely not a game-changer.

A more important breakthrough would be in cost-per-watt-hour. If we saw much cheaper batteries with the same capacity, it would go a long way toward reducing our use of fossil fuels, both in vehicles and in electricity generation.