Yes it would be useful, especially if you are changing a lot of contours.

However I quite like the fact that you can independently drag and move the Hatch itself to various other coordinate positions and I also like the fact that once you've created a hatch you can delete a boundary afterwards, leaving only the hatch - which again can be modified etc..

Maybe some Hatch options could be added to the current drawing preferences dialog - including an option to 'follow' contour or a new Hatch widget created.

Just my thoughts here;)

I never thought of hatching being useful without its boundary. But I admit my imagination may be limited by the fact, that I only draw technical drawings of machine parts. :-)
I am curious what use case that might be.

I agree that some additional hatch options will suit many users with quite different applications of CAD.

I have used hatching without boundaries for laser cutting (etching) patterns/details like brickwork for façades for architectural models and details like ground shrubs/gravel for sitemaps.

This feature request will be closed.
In the use case that was posted, the hatch would have followed the expected change, had it been selected.

I.e.:

1. select only the polyline and drag and drop a node -> only polyline changes
2. select the polyline and the hatch and then drag and drop a node -> polyline and hatch change