I was very excited about the standard gauge subway cars that were announced but never produced. Also, it always seemed like a few tweaks and a couple of parts would have been sufficient to use existing tooling to make an interurban, but MTH had no interest in that either. (However, that should be a great retirement project.)
What the late great Arno Baars called MESG (Modern Era Standard Gauge) toy trains are currently bringing huge prices at auction. There is a market for new standard gauge if new technologies can bring down the costs of production.
Kirk Lindvig