There may well be a drop in motorcycle sales. As a corollary, there may be a rise as well.
While autonomous cars may offer convenience, they don't offer emotion. They are ego free.
Top Minds in the auto industry see the autonomous cars as the destruction of the branded automobile.
Think about how cars are sold, mostly as a mechanism of lifestyle. "Thrill of the road", etc. Cars are bought based on a myriad of factors, not simply safety, not simply gas mileage. Nobody buys a Jeep for gas mileage. Jeeps are sold like Adventure bikes.
So, the theory is that with the autonomous car, much of that will go away. Since we don't own cars anymore, we simply rent time in them, we're less involved with them. We don't care how we look in them, how they perform, what they say about us. Because they don't say anything, most importantly, because they don't say anything about anyone.
But imagine the feeling you had, when you're in your car, and you saw that bike zip by -- splitting lanes. Or watched some bike take off on a road, and vanish behind a corner. The sound of the bike, the dynamics of the bike, the lean in to the turn.
Or the way the rider was dressed. Matching tank top and flip flops. Decked out in back leather. A long beard poking out of a helmet that looks like it's been filled with expanding foam. And most importantly, the independence of the bike. That person isn't trapped in a shiny metal box, a box you don't even have any control over.
Some will certainly favor the security and convenience of an autonomous car, most will.
But many won't. in fact, many who lose what independence they had simply driving their '93 honda Civic, may well be attracted to the independence of a motorcycle, or scooter.
Or, they'll ban them entirely on public roads.