First, let's drop the myth that an engine has to be big to "make money" Disney's two 4-4-0 replicas from 1955 have probably pulled more passengers than any steam locomotives since that time, and anyone besides Disney who thinks they can make money with a steam locomotive should probably seek mental health services - fortunes have been lost trying to do so.
But anyway, here's a local scenario, albeit standard gauge, which might utilize such a replica locomotive:
Between Bennington and North Bennington, Vermont, lies a stub-ended branch line, about four miles long. This is a remnant of the Rutland Railroad's line from N. Bennington to Chatham, New York; the line south of Bennington was pulled up in 1953. Most of the branch has lain unused for 20+ years, and trails people have set their sights on it for removal. It is owned by the state and leased to Vermont Rail Systems, which is presently not interested in parting with it (or subleasing it), but that could probably change with proper financial incentive.
There are two nice depots at either end, one a restaurant and the other restored also, used only occasionally for civic meetings.
Assuming a motorcar group might save and acquire use of the line, removing the heavy brush overgrowth, a tourist railroad of sorts could begin with motorcars. Gradual tie replacement might then allow full size trains to operate there again.
But instead of the usual mish-mash of ex-military 44-ton diesels and battered Amtrak coaches, why not work toward replicating a real train that once ran there? In years long past, there was a shuttle train that took passengers from Bennington to North Bennington to meet the mainline passenger trains that ran between Montreal and Troy, New York. For much of its existance, the shuttle train was powered by a light 4-4-0. A few old wooden Rutland passenger cars from the era still exist, most needing better care and better homes. With a replica 4-4-0, one could recreate the past here. Sadly, an old tender from just such a Rutland 4-4-0 was cut up by the Green Mountain Railroad some years ago, though another still exists behind a Rutland pile driver at Steamtown in Pennsylvania.
Further west,there are two other tourist RRs, former Delaware & Hudson branches that could use a replica 4-4-0 also. The D&H's newest 4-4-0s were rebuilt from camelbacks, with the typical L.F. Loree touches of semi-streamlined design- the last one operated into 1950. As New York State still has some heavy industry, there might even be some possibility for donated services or materials in the latter case, much like the Brits are getting for their replica A1 4-6-2.
Bigger locomotive replicas might also be possible (a Rutland or New York Central 4-6-2, for instance) using discarded parts from Chinese locomotives, but this gets into greater challenges and expense.
