1. Long rental lines at airports. 2. Asking for information that could be provided ahead of time via apps. 3. Having to make your way to the car rental facility.
What I would like and I would be willing to pay a premium for is order the car of my choice via an app. Have said car delivered to my location by a driver that then takes Lyft/Uber back to headquarters. Also it seems like the car rental companies could benefit from economies of scale by having a small number of large lots instead of numerous little lots peppered throughout a geographic area. If this existed, I would use it all the time as I only need occasional use of a car.