No one knows what will happen on difficulty, we only know that the minning reward will be the half, now is 25 Bitcoins and after halving will be 12.5 Bitcoins. Difficulty could increase if minners increase its hash power (if bitcoin price increase like a lot of users think, miners could be interested on increasing its hash power), but if the price of bitcoin is lower than expected its possibly that miners turn off some of this equipment and difficulty could decrease.