On a totally different, also spoilery note, I also wonder how...
They will resolve the war and also Hera's story. In the Appendices, Gondor finally shows up and helps Rohan defeat the Dunlendings after they were pinned down for a while by a simultaneous invasion by the Corsairs of Umbar. I assume that will still happen in this movie, and I wonder if maybe Hera will wind up marrying Beregond, the son of Steward Beren and leader of the Gondorian army that arrived to assist Rohan, who was described as one of the greatest captains of Gondor. It would be a nice way to re-emphasize the bond between Gondor and Rohan that would persist into the War of the Ring and beyond. But they could do just about anything with her, since this specific character isn't actually mentioned at all in the Appendices. The only reference to anyone similar is to a "daughter of Helm Hammerhand," who isn't brought up again after Freca attempted to force her to marry his son, Wulf.