[Weightshift]

Isn't it , by TGM definition, still "on plane" if one end of the clubshaft is pointing at the plane line?

I agree that that plane may not be the most effective for your purpose and that a different plane angle may be more advisable - but it is still technically "on plane".

If you read 1-L-11-6 in isolation you might think so: "The Clubshaft always points at the Plane Line except when they are parallel to each other."

However.. 2-F PLANE OF MOTION All the action of the Golf Club takes place on a flat, inflexible, Inclined Plane which extends well beyond the circumference of the stroke - in every direction. The full length of the Clubshaft remains unwavering on the face of this Inclined Plane - Waggle to Follow-through. Every other Component of the Stroke must be adjusted to comply with that requirement. (Bold by Weighshift)

..and it is the player's responsibility to make it so. There are an infinite number of possible planes but only one Inclined Plane for each stroke.