It does all of this through simple, done-under-the-radar improvement of the old Pennsylvania Railroad mainline between Philadelphia and Harrisburg to 110 mph running.
Right now, Harrisburg is where improvements end, though. This is not an accident. While Norfolk Southern bypasses the former PRR mainline east of the Susquehanna, it uses it -- intensively -- to Pittsburgh. Electrification, and therefore the territory Keystone Service push-pulls can cover, also ends at Harrisburg. And finally, the terrain becomes significantly more mountainous, and the railroad more curvy, as it follows the Juniata River valley deep into core Appalachia's corduroy, up and across the Alleghenies, and back down the Conemaugh River valley.
As it stands, with more operating funds (i.e. enough to purchase a couple of trainsets, engineers, conductors, and slots) integrating a few more daily trains between Harrisburg and Pittsburgh appears perfectly viable. A push-pull setup with an electric at one end and a diesel at the other would also allow these runs to be integrated into the Keystone's existing schedule. And there is the tantalizing possibility of night trains, which Sic Transit Philadelphia discussed a couple of years ago.
And, with relatively simple improvements (bringing back the fourth track, increasing superelevation on the passenger tracks) speed can be brought up for passenger runs, making them more competitive than the Daily Pennsylvanian's current 45 mph average speed.
But that's all for regional trains using the classic track to access the hill towns, towns which have relatively high ridership due to (a) the trains arriving in the afternoon and (b) a general lack of Interstate/freeway competition in the area.* Good regional service is important, but Pittsburgh is a large city and therefore a large travel market; it sits at the crossroads of the Northeast and Midwest; if Pennsylvania wants to compete with New York's Water Level Route and get a slice of that pie for themselves, it's going to need a new passenger route built to significantly more modern standards than the old PRR line.
Through the corduroy mountains.
Approaching the Problem
If Keystone East is an experiment, it's one of the most successful in all of American passenger railroading. It established not only the existence of a rail travel market from a larger city to smaller ones out in its hinterland, it also established that high ridership is a function both of frequent service and a reasonable fare.
But it is also an experiment abetted by advantageous geography and the civil engineering prowess of the Pennsylvania Railroad, and when the PRR electrified their Northeast Corridor in the 1930s, the Main Line section only went to Harrisburg and Enola. Plans to electrify the Middle Division, the section through the mountains to Pittsburgh, were discussed, but came to naught with postwar dieselization.
It's also arguable Harrisburg and Lancaster play outsize cultural roles in the state. Lancaster is, after all, its eponymous county's seat and the heart and cultural center of Pennsylvania Dutch Country (there's a reason Turkey Hill's motto is "Imported from Lancaster County"!) Harrisburg is the state capital ... not much more needs to be said.
Head east down the PRR mainline from Pittsburgh and the same opportunities don't present themselves. Johnstown and Altoona are fair-sized burghs,* yes, but one data-lite argument that can be made is that the relatively greater importance of Keystone East would naturally drive a higher ridership than a similar service profile on Keystone West.
I don't buy this argument. Not because I think population doesn't matter -- it obviously does; more people means more potential riders -- but rather because it attempts to explain a particular result a particular political class doesn't like by avoiding having to deal with, you know, actual data and competent modeling. Data-lite arguments often tend to carry exceptionalist undertones, too, seeking ways any result can be construed as a "special case" instead of looking for commonalities to build generalizations. Alan Garfinkel had a thing or two to say about that kind of reasoning.
All that said, however, it is clearly not easy to get from Harrisburg west. But it may be easier than often given credit for.
The cost of building a new line, as J. Edgar Thomson appreciated when he engineered the PRR's mainline, is a function both of its length and the relative difficulty of its construction. Length scales linearly, difficulty exponentially. This is why he decided to concentrate nearly all of the mainline's most challenging features in one spot: between Altoona and the Conemaugh River's water gaps through Laurel and Chestnut ridges to the west of Johnstown. East of Altoona, the line follows the water level route of the Juniata River; west of Chestnut Ridge, the mainline crosses the Allegheny Plateau while a low-grade freight line follows the Conemaugh down to the Kiskimentas and eventually Allegheny rivers.
Norfolk Southern currently runs heavy eastbound (uphill) trains up the Conemaugh Line and lighter eastbound and all westbound traffic along the mainline. The lines rejoin by Heinz Stadium in Pittsburgh and pretty much anything that isn't a unit train's going to originate or terminate in Conway Yard a few miles down the Ohio. This is a traffic pattern of convenience, though: were there heavier passenger service in the Pittsburgh area, the Conemaugh Line would be able (by double-tracking it again and upgrading the signaling) to bypass most of it.
What I'm getting at here is that, from Pittsburgh all the way to Conpit Jct., where the mainline and Conemaugh Line meet, it's perfectly possible to convert the mainline to a passenger line. Which is useful, seeing how it's a natural commuter and regional rail route. It also offers a useful terminus for a fast passenger route through the mountains at Latrobe, a burgh sitting snugly at the foot of Chestnut Ridge, and where the line curves from following the ridgeline and instead heads directly west.
Like Keystone East, this "Keystone West" uses the PRR's civil engineering prowess to its advantage, upgrading an existing line to high-speed standard. It also offers an easy commuter rail corridor extending from Pittsburgh either to Greensburg, Latrobe, or Johnstown, along with improved regional services along the classic corridor.
This latter is necessary because a high-speed bypass through Appalachia's Ridge and Valley province must be just that -- a bypass. Like all trellis river systems, the Juniata curves too sharply as it crosses from water gap to water gap to be useful for faster travel. Instead, the Keystone Corridor's new middle division must punch through the mountains on an extremely low-curvature corridor.
* The Pennsylvania Turnpike (I-76) runs well south, along the former South Penn RR right-of-way; I-80 runs well north, and if it could avoid trees along with everything else in these parts, it probably would, too.
** The combined population of Harrisburg (49,673) and Lancaster (59,322) is 108,995; their MSA's, better for intercity planning, are 509,074 and 507,766 for 1,016,840. For Johnstown (20,978, 140,499) and Altoona (46,320, 127,089), that's 67,298 and 267,588.