I was thinking about how product roadmaps evolve a little like Maslow's hierarchy of needs.

"Deficiency needs must be met first. Once these are met, seeking to satisfy growth needs drives personal growth."

Product roadmaps first focus on deficiencies and then growth in a tiered hierarchy and if a deficiency appears we must first have this satisfied before we can focus again on the growth needs. If we don't have shelter or food, we don't need "security of body" or "lack of prejudice". These features jump to the front of the product backlog in scrum terminology.

Take for example a software product that helps site operations personnel (siteops) manage a colo of 1000 servers.

The first set of needs will be "What do we have?" (stock tracking) and "What is broken?" - (focus is now)

The next tier could be "What is connected to what?" and "What redundancy do we have?"

The tier that follows could be "What spare slots do we have?" in terms of rack space, free ip blocks - focus on forward planning and "How many more servers do we need to order given predicted growth and load?" - capacity planning
The next tier might be about virtualisation - vmware - the ability of applications anywhere and move them freely.