Many other cubing timers allow for creating custom "categories", e.g. named subsections under 3x3x3. Speedcuber Timer handles many of the most common use cases for those categories by having a wide variety of events built-in.
However, there may be reasons why someone would want additional sub-filtering, so I propose adding a tagging system. Essentially, users can add a set of tags that will apply to every solve until changed, and then support filtering by those tags on the attempts list and the insights charts.