Well, several of us here have different pedal systems on different bikes. I had my mountain bike with SPDs when I got the Speedplays and I also had SPDs on the Jamis Coda I had for 3 years. I didn't have any trouble switching between something that was already ingrained and the Speedplay Xs. Then I sold the mtb and Coda and put Speedplay Frogs on my custom road bike as I wanted to be able to wear mtb shoes on this bike. That was a bit of a curve because it is so easy I kept unclipping by accident.
I have 2 pairs of shoes, which is worth it and I also kept the cheap level Sidis I had with SPDs for the occasional spin class.