Always thought that India or Indonesia might make a superb, and very unusual basis for a layout. In both cases you had steam locos of American, British and mainland European origins operating side by side, some ancient, some modern. With severe lack of investment in the 70s, 80s and 90s, these places were not unlike Ireland in the early 50s, with services operated by genuine museum pieces, like Sharp, Stewart 2.4.0 tender locos built in the 1870s operating in Indonesia (Java), meeting main line trains at junction stations (like Madiun) hauled by Alco or GE diesels of American origin, or huge 2.8.2's built by Henschel in 1953.
A layout with fantastic contrasts.
Meanwhile in India, a 5'6" gauge streamlined pacific, not unlike 800 "Maedb" in size and performance, would sweep into a junction station like Neral or Gwalior, where a tiny 2ft gauge loco (perhaps a Baldwin 2.8.4) would await across the platform. I was at 3 or 4 places in India in the 70s where scenes like this could be seen.
Another feature of these scenarios is that you would see an apparently idle loco in steam, or an elderly black-smoking diesel, setting off from weed covered sidings with a single van to go up the line to the next station on a short "trip" working in between normal trains; even in layout form, the relaxed and occasionally chaotic nature of operations would be captured perfectly.
Just a thought.