Seems like many of us begin with "Layout Planning" with an overall design concept that includes terrain ideas. Then work out the details of the "Track Plan". Next, fill in the imagined terrain details, making adjustments. So "Track Planning" is only a portion of the design process within the larger design of "Layout Planning", and in a sense terrain ideas are actually included at the beginning of the process, kind-of like the terrain already existed. Of course during construction, most of us then construct and test the track first and then add scenery after.
I suppose the proposed idea could be attempted with rough-ed in foam scenery, which can then be carved and filled fairly easily as the roadbed is pushed-through and then track laid. On the other hand, I am always eager to get some trains running as a first priority
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I also tried G gauge in the backyard years ago, and had an operating layout for three years. I found it to be too difficult in Georgia's heat to keep the layout running. The sun's heat plus the energy on the rails tended to expand the rails significantly, and the higher temperature increased resistance to the current. It was pretty cool when everything was working. Perhaps battery-powered G would have worked better.
