The new coach has to settle the QB position first and foremost before they can contend. No small task.
There is some younger talent on offense and defense to build around, but there is going to be a lot of questions about the "big money" guys that could cloud the transition from Tomlin over the next year or two.
Heyward and Watt, in particular, moving on could create somewhat of a leadership vacuum the new coach will have to deal with.
Despite all that, the patience of the Rooney's is probably what makes the Steelers job as appealing as it is.
Unlike with many other teams, the next Steelers coach pretty much has zero chance of getting fired within his first few years, no matter how bad things are.
Obviously, he won't be guaranteed 19 years, but will pretty much be given his entire first contract to install the roster and system he wants.