It is possible to create new Dimensions for use in Dynamic Reporting by adding Profile fields to a Sending Logs Extension; these added fields will then appear in the Dimensions area. Here is an example in which we extended the sending logs with our custom fields "Is Employee" and "Is Student"; these then became available as Dimensions.
However, the only Segments available in Dynamic Reporting are by Age, and there is no way to create more Segments.
It would be beneficial to allow for the creation of custom segments for use in filtering report results. For example, we could create segments for various regions across the U.S. by grouping several states into each segment, or by distance from a certain location (i.e. under 50 miles, 50-99 miles, 100-200 miles, etc.), or even by age ranges other than those provided (such as splitting 18-25 into 18-20 and 21-25).
Custom segments should not be specific to a single report. Like the custom Dimensions, they should be usable in any report.