If I were going to set up a train garden, I would choose a scale where I could conceal a video camera in the locomotive.
I'd also like to arrange for some remote control cars, in a controlled (garden-like) environment, where you could see through a video camera what the car's windshield would reveal.
That could make some fun out of competitive racing games.
Wow! That sounds fun! Good idea!
Garden railroading is growing. Because of the difficulties with running electricity through exposed rails outdoors, many garden-railroaders use larger-scale models that can house rechargeable batteries and run them via radio remote rather than through-the-track power. The larger scale track and rolling stock are also preerred for their greater durability in an outdoor environment. A few have even discovered that animals, both wild and domesticated, are REAL threats to their down-scaled rail empires. Your resident viking kitty really DOES look fearsome to the brakeman on a G-scale garden pike!
I've seen video cameras advertised for use in HO-scale trains, though, if you mounted it in the cab, it'd have to be a modern diesel or a Souther Pacific cab-forward for you to have much of a view. I know I've seen at least one ad where the camera came pre-mounted with the lens poking out the nose of a locomotive -- presumably you could chose the roadname and paint scheme. That would at least provide an unobstructed view of the tracks.
I like your through-the-widshield idea, too, but I'd like to see it applied to larger, gas-powered RC racers.