Many organizations will fail in their efforts to create an IMA. The following is a partial list of roadblocks that might thwart your attempts in your enterprise.
This is a significant problem in many enterprises. Years of poorly managed projects and expectations may have left business units with antipathy or even hostility toward the IT organization. IT organizations, being made up of human beings, respond in kind. The end result is a dysfunctional situation that sinks any proposal from IT.
You will need to decide whether the process for creating an IMA is one that will help mend that rift or whether other, more fundamental steps need to be taken first.
This fear is often expressed as something else, such as lack of support. IT organizations may fear that they are giving up control of decisions they've always made (like those surrounding security) to business units.
Business units may fear giving up their data. For example, if HR has always maintained the employee database and you start talking about creating a metadirectory where multiple players will have access to or, heaven forbid, the ability to change employee data, you're likely to get significant push back.
Part of the process of creating an IMA is aimed directly at giving everyone a voice and being able to work through these fears. The process should be targeted at creating consensus around key principles regarding identity processes and data, and how they're managed.