Tesla hopes autonomy subscriptions can deliver the margins car sales cannot.

Elon Musk’s “flying” Roadster jumped and flipped through the air this month in a stunt that went viral around the world. But his bigger bet is on changing the way Tesla makes money—and the wider car industry is scrambling to catch up.

Five days after the spectacle, made possible by compressed-gas thrusters developed by Musk’s SpaceX, he revealed the companies were exploring a merger that could accelerate his push into autonomous driving.

At stake is more than a technological race.…