Consider California [1], where it'll likely cross that in the next few years.
2015 | 1.7%
2016 | 1.9%
2017 | 2.6%
2018 | 4.7%
2019 | 5.6%
Or Norway, where it is already at 48% [2]Both have higher gas prices and subsidies that help with TCO comparisons. But EV costs have lots of economies of scale yet to achieve.
Hard to imagine it takes 10 more years for the rest of the country to catch up to California.
[1] California New Car Dealer Association report Q2 19 https://electrek.co/2019/08/19/tesla-sales-electric-car-mark...
[2] https://insideevs.com/news/357526/june-2019-plugin-sales-nor...