Numerically speaking, compared to the numbers of boxcars in service years ago, the general purpose boxcar is basically dead.
I owned one of the early 2000's BNSF diesel roster books, and it included a brief discussion that the railroad had gone from owning about 7000 general purpose boxcars down to basically zero within a year or two.
Many of the boxcars that remain are considered by the rail industry to be "specialty" boxcars. They have a specific cargo they carry and may be captive to a specific industry--like Auto Parts or Newsprint. Trains magazine carried an article a couple years back that basically said most of today's boxcars are specially built for a specific purpose--and if that purpose goes away, they may get scrapped.
Here in PA I've seen long lines of old yellow 1970's Railbox general purpose boxcars in storage a couple years ago. Since those cars are approaching 40 years of age, the end of their effective lifespan (some cars are not allowed in interchange service between railroads after 40 years of age--tank cars get an extra ten years, I'm assuming due to the complexities of the coatings, etc. inside them) is fast approaching. I have noticed recently that the number of Railbox boxcars in actual service--moving through Enola Yard on a daily basis--is less than it appeared to be just a couple years ago.
Obviously there are former Railbox cars out there in their second, third, or fourth paint schemes, but those numbers are declining and I suspect that many of them are carrying the paper products as they are often seen in cuts with the known (and still fairly common) Canadian newsprint boxcars and the new TTX yellow hi cube boxcars built specially for paper service.
So, I see boxcars in the yards--but out on the NS mainline they appear to be greatly outnumbered by containers of one kind or another, either single or double stacked, or trailers.
John
