I am left handed. My machine actually doesn't have a floor pedal, it has a lever that attaches to the stand my machine is in and is pressed to the side with my knee- it's on the right side. It's all I've ever used for a machine and it feels natural to me. I do think that I'm a little ambidextrous when it comes to which of my feet are dominant, though- when I played soccer in high school, I definitely favored my right foot, and when I did ballet going on point on my left foot felt more comfortable. I guess maybe I'm a little mixed up, lol!
I do think that people are pretty adaptable, though- when someone has to have a limb amputated, they learn to make use of the others pretty quickly! I'm sure you could adjust to using the other leg if needed.