Way too much is being made of Payton's previous way of handling RBs. There's a reason they went out a got the top-rated RB in the draft & spent a 1st round pick to do so. 1st round picks are like gold, especially when you spend one to get a RB of all things on a team that needs defensive help for the most part. They have an outstanding offense, but the Saints evidently wanted a stud RB to make them even more effective on offense. WIthout a top D, they basically need to outscore opponents. If the Saints were going to stay with a RBBC, there's plenty of RBs in this draft which would've adequately augmented Thomas, Sproles, & Ivory.
We all know RBs are one of the most injury-prone positions in football. Obviously, the Saints know that. They're the defending Super Bowl champs trying to repeat, which is extremely hard to do, & want to be prepared should Ingram go down. It can happen. That's the reason for the extra backs. Simply put, should Ingram go down, Thomas, Sproles, & Ivory would be needed to keep the offense at a high level in Ingram's absence. I'm sure those guys will get some touches, but I have no doubt they plan for Ingram to eventually be their feature back.
All that said, I suspect Ingram will be somewhat slowly integrated into that role. Despite all his talent, Ingram is a rookie in an intricate offense. By mid-season or so, I believe Ingram will be getting the vast majority of touches. At the very latest, the start of next season.