Searching eBay for monorail stuff, I discovered that in the 1970, Mattel produced a futuristic train set called Hotline. The range included track, a loco, wagons and coaches. Powered by an onboard rechargeable battery, the loco was a 4-2-0 although since it was supposed to be jet powered, I'm not sure Whyte notation applies!
Anyway, a little digging and I find these videos:
Fantastic stuff. Who wouldn't want one of these?
I notice that they were only sold in the US and that might be because the space required for the track is as big as most UK lounges. The film maker has had to clear his of furniture to install the track. Mind you he also makes reference to running out of time and I wonder if there is a family on the way back who wouldn't be too pleased to see futuristic train set all over the floor.