Please add the ability to add constraints on a sketch to previous sketch entities.
Allowing a sketch to reference/constrain to a previous sketch allows for an initial layout sketch to drive subsequent features without having to extrude a shape initially.
It would also allow references to parts of an early sketch prior to being modified by new features (i.e. pick up the corner vertex even after a fillet has been applied).
The existing sketches are visible and clickable when making a new sketch, but constraints can't be made between the current sketch and the existing sketch.