Totally agree that taking out a pocket door (love them too!) and replacing with a barn door is sacrilegious. However, I disagree with the thought of how it started.
I believe a barn door is the perfect solution when you have a pass-thru opening (say between a master bedroom & master bathroom) and would like some privacy, for whatever reason. Many new homebuilders are leaving this pass-thru as is (just drywall), and unless you pay for a door before construction, you have no other alternative unless you hire someone to frame the opening & install a new door. Many homeowners aren't that handy, but by the same token, many can and do install a simple rail for a barn door.