I think is desiderable sorting or grouping by focus in filters.
For example, you can make a filter with the actions have been not prioritized and it's important to know if the actions are inside someday focus or inside others.
In general, not only in advanced search you could be able to sort and to group by any of focus, project, goal, context, starttime, deadline, priority, etc.
Thank you very much for your proposal!
The feature of 'Group by Start Time' is similar to what you need. So maybe 'No Start Time' group under 'Group by Start Time' can be divided into 'Next', 'Someday', 'Waiting'.
We'll have a discussion about this.
Have a nice day!