It might be easier to change today than it was in 1886. Back then, trains were really the only means of travel between cities. Today, there are less passenger trains than back then, though more freight (even with trucks and planes). But freight diversions/delays could be scheduled well in advance and have alternative means. Not to mention, since then we've developed variable gauge train tech. A subset of trains could run during the cutover.

It's likely more costly today, but less disruptive.