Someone mentioned the 1E ranger and that sparked a memory. Back in 1E the ranger's biggest edge was tracking. It was an often critical skill, and the ranger was the only one who could do it. With subsequent editions opening abilities to more classes, the classes that had a showcase skill like this have lost some of their raison d'etre. The other big example is the thief, whose climbing skills were critical in 1E, but in later editions have had a declining edge in this department. The 5E ranger is a bit better at tracking than other classes, but not enough to matter much.
I would like some of these unique skills to return, but then you have the issue of what happens when noone wants to play that class. In my games I would expect the players to get creative and come up with alternate approaches, but what about games where the players decide they have to be able to track for some encounters they want to do? One idea would be to allow all classes to have an ability but to impose a higher cost outside of the class for which that's their "thing." Frex, tracking and climb walls require a feat, but the ranger and rogue, respectively, get it for free.
What if Rangers (only) could circumvent pass without trace? And perhaps, at later levels, they are the only ones who can find someone using an Amulet of Proof Against Detection and Location?