I've not seen any discussions about Favored Enemy and Studied Target being interchangeable. Probably because they don't really have anything to do with each other, unlike bloodrage/rage and bardic performance/ranging song who uses the same mechanics.
As I was saying though, they don't use the same mechanics because it is clear that the designers are getting away from the flat Favored Enemy bonuses (which many players thought underpowered). The deluge of "Studied Target" archetypes compared to the complete lack of Favored Enemy ones is a good example of this.
But it's clear here that this hasn't been discussed, so maybe it's time. That's as much of an answer as anything - my search-fu wasn't terribly weak, it's just not been asked.