The following blog post summarizes the sixth chapter of the Product Roadmaps Relaunched book by C. Todd Lombardo, Bruce McCarthy, Evan Ryan, and Michael Connors. Published on November 28, 2017. The sixth chapter is reviewed and summarized using my best judgment of the most essential information.
On a theme-based roadmap, you can include additional information to your themes, subthemes, customer needs and system needs. Even though your roadmap is important and useful without this additional information, including some of these pieces may help sell and align key stakeholders on your roadmap.

Features
This may seem contrary to the previous chapters of this book. It would be best if you targeted your roadmap to be theme-based, focusing on the needs of the product, not the features. But in some instances, it can be helpful to list features. Typically, when features are listed, they appear as subthemes or additional information to a theme to demonstrate that it is not the focus but a possible solution to the problem. So in the following cases, it is appropriate to include features:
1. Including probable solutions
It is okay to list a probable solution on your roadmap even if it is not validated. This is because, at this point, clarifying what is most likely to be used can help stakeholders buy into the idea. But you’re listing it as a subtheme to reduce focus on the solution and to communicate that it will support the main theme.
2. Including infrastructure solutions
Similarly to probable solutions, infrastructure solutions can also appear on your roadmap if a probable solution is identified.
3. Including carry over solutions
Lastly, it is common to see themes carry over from previous iterations of a roadmap. It is very difficult and near impossible to accurately determine when tasks will be completed. So, when this inevitably does happen, some items of your roadmap will appear on your next iteration. Solutions to certain themes may have been validated at the previous iteration; therefore, they can be included in the roadmap at that point.
Tags
You can also include on your roadmap a stage of development tag. This tag can indicate at what stage of the development process various items are in to better explain and visualize when those items will be delivered. A confidence tag is also very commonly used. Confidence can help convey how likely you are to deliver that item in that roadmap iteration which helps set proper expectations with key stakeholders. Target customers or Personas can also be tagged on your roadmap to show which items address which customer groups. Lastly, Product Areas can also be outlined in your roadmap to show what areas of the product are being addressed (back end, mobile, etc..).
In summary, on a theme-based roadmap, many key pieces of information can be listed above and beyond your themes and subthemes. But, you can very easily over-complicate your roadmap by including too much information. Therefore, choose wisely what information is essential for your product and organization.