I would like perspective grid snapping for either the brush and/or the pen tool.
Although shapes can snap to perspective this is difficult to line up intersections and feels unintuitive to those of us used to lining up a ruler on pencil and paper.
In my mind the snapping would work similar to holding down Shift to snap to 45 degree direction, but instead when you hold down which ever buttons enable the perspective snapping, the drawing tool moves in the perspective direction closest to how you move the cursor.