What we could do it simply rotate the current WP so the current axis direction becomes the edge direction (we still need to define which direction, as a linear edge can have two). The rotation around the edge will be rather uncontrollable, though...
I would prefer the normal and binormal vector to define the coordinate system for the plane.
I work with this direction tangent/normal or tangent/binormal here https://www.youtube.com/watch?v=fScyrV9fB80
So the thing would be for ex. to select two edges, or an edge and a point... But then, the user could want to place the plane coplanar to it, not perpendicular...
I think this begins to bee too many options for the working plane tool. Maybe a better path would be indeed to integrate the workplane WB tools better in it?