Early on -- back when del Toro was doing it -- they said they were going to pad The Hobbit out into two films by including the stuff about the White Council going after the Necromancer south of Mirkwood, all of which is mentioned in passing in the text. One would assume that this is why you're seeing them on set.
I'm not in the least bit flustered by the changes, but I'm not terribly excited about these films, either. Thanks to stuff like the DC animated universe, I've come to view adaptations as their own thing. However, Jackson does not excite me as a director at all, he more or less lost me with RotK and Kong- especially the latter.
I can accept that this is going to be PJ's prequel to PJ's LOTR -- though I would rather have seen Del Toro's take. Or maybe a director and studio who were completely divorced from the LOTR movies. Maybe in twenty years.