Actually, Iniesta could very well be the starter next season as well, but starting with 2016, he needs to go into a more quiet role inside the team. Say what you may about the Pogba deal, but money aside, if we sign him from 2016 we will probably have that LCM position set for some years to come. Imagine Pogba - Neymar on the left for about 6-7 years. It doesn't get better than that for me. I would very much like us to remain with Iniesta-Rafinha for the majority of next season, and add another midfielder in this winter to take care of the right side of our midfield along with Rakitic.
Let's not forget we are now one midfielder short compared to last season. I'm all for signing Arda Turan right now and have him ready to play in the 2nd part of the season. If we catch an injury in the midfield, as things stand right now, we're in big trouble. I hope a top midfielder will come in january and that he can play in Champions League (the real Champions League starts in february anyway). Iniesta, Busquets, Rakitic and Arda Turan (maybe Masche too, if Vermaelen shows he can be trusted as a CB -- as usual I don't really trust Mathieu) is a midfield that can do some damage IMO. Turan is much much better than people give him credit for and I think he'll be great for 3-4 years for us. Splash the money and get him. You can't have such a big difference between starters and squad players right now, and out of all top teams, the difference between the starting 11 and the rest of the players is too big in our case. We were lucky we weren't plagued by injuries (credit to Lucho as well), but things can change next season and we need to ready to tackle whatever problems may come our way.