I had the Gem HO 2-4-4-2. They called it a Baldwin Mallet or Little River. The Gem version was poorly made and I had to rebuild the whole thing just to get it move. The better one was made by Akane. No reason it couldn’t be done in O scale standard gauge. As pointed out above it already been done in 2 rail and On30. Not sure why anyone would say it wouldn’t sell. Look at the 0-6-0ts flying off the shelves. Not exactly a stunner.
Pete