In The Hobbit, my feeling is that JRRT used Beorn for his somewhat conventional fairy-tales aspects, the skin-changing, as TH was closer to the conventional fairy-tales than anything else he wrote. Closer, but even in TH, there were some aspects that were unusual for the convention of its time. The bit about Beorn’s “treatment” of the goblin and the warg he had caught wandering: “A goblin’s head was stuck outside the gate and a warg-skin was nailed to a tree just beyond.” For a certain quarter of supposed educators very busily PC-scrubbing old fairy-tales recently, this would have elicited shrieks of horror, and would have consigned TH to the index of forbidden books. And make no mistake about it, anything which ended up in the collections of the brothers Grimm etc. had already bee sanitized for at least 19th-century tastes.
But lurking in the background with Beorn are not a few warriors in sagas and whatnot, totally unsavory by today’s standards and only usable in FSK-18 rated films in Germany (FSK-18 is the max, and is only used for the most violently gory of movies; a kind of X rating for violence). Even Beowulf is quite a savory character by comparison. If I just compare Verlyn Flieger’s 2015 “Kullervo” with how JRRT transformed that into the story of Turin, none of the saga berserkers (meaning “bear-shirt”, I believe, and what Beorn effectively was) would have made it into JRRT’s legendarium without some heavy reworking. Only in PJ’s films does something of the berserker madness turn up, transferred to the baddie side in the suicidal berserker Uruks, like the one that lighted the “gunpowder” which breached the wall at Helm’s Deep.
So Beorn in his aboriginal berserker aspect was a no-go for JRRT, probably. But for the between-Hobbit-and-LoTR TV series planned by Amazon, while Beorn is dead, being mortal, by the time of LoTR, there should be several decades of overlap in the lives of Beorn and Aragorn to be able to work Beorn into this TV series. But then again, that’s a different thread here on A-U …
So the chieftan thing was only after the hobbit. That makes a bit more sense in my mind. 
