There are two new properties for subgroups:
Passthrough
The default subgroup first blends the strokes locally within the group, and then blends the group with previous strokes.
Passthrough mode basically blends the strokes in the normal order as there is no subgroup there (while you can still operate the group of strokes as a compound object).
Overridden
Overridden mode overrides the contained strokes with the subgroup's own color and material (A/B).
It's often used when you only want to use the subgroup as a single stroke with customized shape.
Duplicate Strokes in the Stroke List
you are also able to duplicate strokes directly in the stroke list by dragging strokes with CTRL+SHIFT pressed.
These features will be first updated in the prototype tier of this month.