Gradually!
Some classic Jaguars had the pedals switched - including the famous one in the Inspector Morse TV series which led to a few accidents on set.
Porsche also made some race cars with the accelerator on the left to make it quicker to do 'Le Mans starts' - where the driver must run to the car and start it.
Didn't they used to jump in, either over the side door or through a window, both feet would reach the footwell at about the same time; arguably from the angle of attack the right foot might be first to the pedals. I suspect it's more to do with gearbox placement or similar.
Porsche also made some race cars with the accelerator on the left to make it quicker to do 'Le Mans starts' - where the driver must run to the car and start it.