When the Railroad Museum of Pennsylvania was being established the late '60s, there was some serious lobbying to locate the museum at the Northumberland roundhouse. Penn Central wasn't using the roundhouse for regular operation and the place was basically a time warp; in addition to the roundhouse, turntable and yard, there were still-extant water tanks and coaling tower, auxillary buildings, etc. Ultimately the decision was made to construct new facilities next to the resurgent Strasburg Railroad, which was already leasing PRR D16sb 4-4-0 #1223. There was also some thoughts about the feasibility of relocating Steamtown USA to the site at one point during the "We've got to get out of Vermont" phase. Pennsy fanatic Don Ball Jr. was likely quite aware of the possibilities of the Northumberland site during his tenure as director, when he oversaw the .
Unfortunately, there were some serious issues wth the site:
First, the roundhouse, and the yard by which it was surrounded, were in a flood plain. It's one that takes a bit of doing to flood, but it has definitely happened in the past. There are said to be photos of the turntable pit being pumped out post-flooding.
Second, the roundhouse, at the time, was surrounded by active railroad trackage and yards. The nearest road access is via approximately 1.5 miles or more of private road through a railroad yard. If this museum had been opened here in the 1970s, it would have mandated its own access road and overpasses, infrastructure costs that might have dwarfed even those of restoring a decrepit roundhouse or those of the Steamtown NHS.
Third, Northumberland itself was very badly situated and equipped for auto traffic and tourist demands.
And for what? You still don't have a track on which to operate, since PC and Conrail were still using those rails, and while it's no terribly busy today, NS still uses the yard as a switching yard for local traffic and interchange with the "Robey Family" cluster of short lines in the area. Sadly, the roundhouse, turntable, coaling tower and other legacy structures were all yanked down by Conrail in 1986.
However, the damning problem is the same: You could put the current RR Museum of Pennsylvania beside that former roundhouse, and operate in a portion of the yard Spencer-style, and it still would only attract meager visitorship on the same level as Steamtown, nowhere near the levels of the current Strasburg location. And if Steamtown had gone there, any hopes or chances of excursions would be pretty much dead and buried.