Well, with the failure of the Santa Fe 2-6-2 to generate much interest, I think more Santa Fe steam is only wishful thinking for a while, so don't faint, I am actually going to suggest foreign line engines.
Frisco had very neat and well-maintained locomotives. I could get a Frisco caboose or three Frisco passenger cars and use a small Frisco steam engine on an imaginary train on the high plains. Even better would be an engine from the Frisco subsidiary, Quanah Acme & Pacific. I think they both rostered 4-6-0's.
But Scott has tried to offer Frisco in the past, and not enough interest was forthcoming. So, something that might sell and I might buy would be a Southern Pacific 4-6-2. Scott offered such an engine, oh, I don't know, maybe 10 years ago. Maybe it could work again, especially in light of the Harriman cars recently produced.
I won't hold my breath, though. Big 4-8-4's and articulateds seem to be what the market wants.