Road maps are difficult to maintain because like a garden they require constant attention. IMO the Alfresco road map is much better in terms of freshness of content and verbosity than may other OSS projects but there is always room to do better. This is just one thought about an organization for the roadmap that may be able to satisfy a number of competing factors.
provide a high level direction for where the product is going (CIO/CTO level summary) -- OBJECTIVES
Provide a summary of each feature as it relates to the objective (Power users and Programmers)
Provide a best effort schedule of what features will be released in which product release (PMs, Power Users and Programmers.)
It seems much too difficult to combine these functions in to a single listing. The proposal below breaks them out in to sections.
Example Road Map
Paragraph about what feature A is and maybe short description about how it meets objective if it is not entirely obvious.
Paragraph about what feature B is and maybe short description about how it meets objective if it is not entirely obvious.
Paragraph about what initiative C is and why it is (example refactoring) and maybe one line about how it meets objective if it is not entirely obvious.
Paragraph about what feature D is and maybe short description about how it meets objective if it is not entirely obvious.
Initiative C (linked to above for single description). Short description on how it meets objective if not entirely obvious.
Features and initiatives are added to the release timeline as they are understood and can be appropriately scheduled. The timeline is a best effort estimation and not a hard guarantee that a feature will be in a release. In an effort to be transparent it may be helpful to provide a level of certainty that the item will be in a given release and in terms of the release, that it will make its given target release date.