OT: Development of the Business Case: 2
At the same time, the intended products are identified as far as possible through the necessary customer/user input.
I don't think this is realistic. You can't afford the time to plan in sufficient detail that you have identified all major products before program management decides which potential projects should be done. What happens if you have 20-30 potential projects? This is where you get those far-too-optimistic so-called project plans - optimistic because the planners are at too high a level and haven't thought of all the sub-products that would be needed.
Again, I think we have a different view of the role of the project life span in the evolution of a project, its major stage gates and their respective milestone criteria. Selecting from amongst multiple projects is the emerging discipline of project portfolio management that is a corporate responsibility and beyond the realm of project or program management.