So what's likely to be in the 2nd Hobbit film?

Well for starters... not many hobbits, if any. I suppose there might be some sightings of Bilbo in the Shire doing not very much in the 80 years (I think the LotR movie made it 60 years) between the events of the Hobbit & the Lord of the Rings. I guess we might see him adopting Frodo at the end.

I must admit I'm doing this from memory & what I've gleaned from different sites in the last few days, but there's enough plot in the appendices of the Lord of the Rings to make a decent movie, just no dialogue nor characterisation.

So what've we got?

From events that took place during the Hobbit, but only mentioned in passing by Gandalf, we will almost certainly see the White Council meet to discuss the "Necromancer" at Dol Guldur. The Necromancer is Sauron returned. Gandalf leaves the dwarves & Bilbo at Mirkwood, and enters the Necromancer's lair. Later, the White Council drive him out & he regroups in Mordor. (this will be in flashback as it occurs either during or before the events of the Hobbit).

We should see Galadriel & Saruman in the White Council scenes.

From the appendices of the Lord of the Rings:

Aragorn meets Arwen. Serves with the Riders of Rohan & also in Minas Tirith. Spends years hunting for Gollum in the wilderness.

Gollum searches Middle Earth for the thief Baggins. He is tracked and caught at various times by both Aragorn & the Rangers, and Sauron's forces. Gollum is tortured by Sauron for news of the ring & Sauron begins hunting Bilbo.

Gollum meets Shelob (the big spider).

Balin, one of the dwarves accompanying Bilbo on his quest, leads a group & recolonises the lost undergound city of Moria. Remember, there's a big fight at his tomb in LotR? So we should see Moria in all its glory, then being destroyed by the Balrog that fought Gandalf.

Saruman begins to turn to the Dark Side & becomes a Sith Lord (Oh wait....).

Gandalf begins to suspect what Bilbo's magic ring really is.

I'll add more as it occurs to me, or I spot it elsewhere.