I think we could have some switch in sisterly relationship with Prim and Katniss, sure. It's understandable if Prim is coming into her own and taking on more responsibility while Katniss may feel left out, and without Peeta (despite probably not liking him) and Gale maybe being more distant if he's with Prim so much. 

That works for me. I think we could have Coin try and capture Katniss for her own reasons when Katniss was meant to stay hidden from district to district, so it could be a sort of three sided war, rather than the two sided one we had going on the books.