FWIW, here's what I did. I can't ride without clipless pedals because it feels weird, my feet slide around and I go way slower. My clipless pedal of choice is the Speedplay Frog, so I put a pair on my Brompton. The nice thing about the Frogs on the Brompton is that they are relatively small, and there are no sharp bits, so it's not really a big deal that the left pedal sticks out when folded. And if need be, it's easy enough to spin the pedal off with a 15 mm wrench and thread it into the inside of the crank to make the folded package smaller or fit the Brompton into a bag. If you find a similarly small, non-sharp and easily removed clipless that's to your liking, try that.