Many thanks to Jamie, Matej, Gerry and Jiri. I daresay most of your ideas will cover various kinds of fejetony and in practice IMO various overlapping categories are applied in the English-speaking world, e.g. opinion column, opinion piece, commentary piece, essay, mini-essay, part of a magazine programme - or no category is used at all and these slots are just referred to by some zippy title or not even that. Wikipedia notes: The radio equivalent of a feuilleton is a fixed position of a slot in the time layout of the transmitted programme and the use of different kinds of conventionalized signals, like the author's own voice, the same title of a slot, etc.
Surely an editorial is written by an editor or at least someone nominally in charge. I agree that a columnist plays the role of a regular feuilleton writer, but this does not transfer so easily to the radio medium IMHO because a radio column first and foremost suggests to me at least a printed column about what is on the radio.
I agree with Matej that the original fejeton had a very individual point of view and was not too weighty (Neruda wrote some nice ones too) but that nowadays it can refer to current events and/or whatever is on your mind at the moment. "The tone of its writing is usually reflexive, humorous, ironic and above all very subjective in drawing conclusions, assessments and comments on a particular subject." Wikipedia on feuilletons.
Course, nowadays we all have blogs and everybody is a feuilletoniste, so the idea often remains implicit IMHO. :-O