As a for profit business case? No one does not exist just like one does not exist for all of the other state supported corridors.
Boise is the Capitol, and a big college town that is growing big time. I loved my visit there earlier this year. Really lovely town.
I’m quite sure the ridership numbers would be high.
Ok, I've got to disagree on the lack of a case existing for
all of the other corridors. The Lynchburger, in particular, has often shown a
very strong profit margin and I strongly suspect that were we in 1974 instead of 2019 NS would be looking to acquire equipment to expand service. Note that the numbers for that train are such that it
probably covers the cost of equipment acquisition.*
The other VA services are in a similar boat to varying degrees (though the question of the Richmond/Newport News/Norfolk trains is inherently rather tangled at the moment owing to the mid-year schedule shuffle), but taken as a bundle you have operating costs of $51.8m and operating revenue of $64.2m (and thus an operating ratio in the ballpark of 80%)**. That is
probably enough to cover equipment orders; the question of track improvements is trickier, but at the same time
that question is muddled by a tangle of questions involving the mixed use of any improvements (freight, commuter, and intercity trains all arguably getting benefits) and the question of what improvements would be merited versus what is being demanded by the host(s).
For the record, I do also believe that on the numbers available, the Norfolk extension is probably creeping up on a point where it justifies its full costs. The margins on equipment costs for the three affected routes (Richmond, Newport News, and Norfolk) probably aren't
quite there (at current margins, the operating profit would probably be sitting somewhere over $200m over 25 years...definitely enough to cover probable equipment needs, but we could go back and forth as to just what those needs are versus what share should "belong" to Amtrak for the portion of service north of Washington) but it seems like they're pretty close since I
think the cost of the Norfolk extension was in the $100m ballpark per the agreement of NS.
*Yes, I am well aware of the complications of VA's contract with Amtrak here in terms of revenue allocation and I'm not sure how a similar arrangement would have looked either pre-Amtrak or in the early years of Amtrak versus what VA worked out.
**I'm also aware that there's some oddness in questions of what ticket revenue is on some of the routes versus total revenue and whether there's a state subsidy buried in any of the trains' numbers.