There were ready-to-run R/C vehicles in a close to O-Scale size a number of years ago. The problem is that almost all RTR R/C's of anything less than hobby-grade have what I call "binary" steering and throttle--either full or off. Full-speed or stop, steer all the way left/right or straight ahead, Not the sort of thing you'd want on a layout.
The ironic part is that proportional steering and throttle were more common in late 1980's-early 1990's RTR R'C's than today. Below is one of my smallest R/C's with proportional steering and throttle, an XMods Honda Civic offered by Radio Shack, pictured next to a scale Allegheny for size comparision:
Granted, you could transplant micro-RC electronics into these toys if you're handy with adapting the mechanical guts to hobby-grade receiver/speed controllers and servos. I plan on doing just that to a small collection of Chinese R/C buses I've acquired over the past few years (they're a bit larger than O gauge--more like 1/24 scale).
One potential fly in the ointment is the growing scarcity of speed controllers that work with plain brushed DC motors--the R/C crowd appears to be rapidly moving toward the use of brushless motors that require specialized speed controllers. Retrofitting a brushless motor to a toy-grade R/C of a size useful to our layouts would require fabricating new motor mounts and installing pinion gears compatible with the existing toy transmission, something I hope to not have to face.
---PCJ
