Hi James

>> Does existing Construct2/Blend node work with your "Select_SubObjects" node?

No, It needs two named edges to work and it is not easy to use either. Also, it doesn't have an option to flip curves or edges.

>> Maybe a similar approach is required for offsetting and blending.

I've made a new blend node that works with "Select_SubObject" node on edges and curves.
Also, offset node works really nice with edges, faces and curves. :)
So, there is no need to add new nodes except "blend" node.

Some new options I'll try to add:
An index input and output for "Select_SubObjects" node instead of adding it to the other nodes.
A "sharp points" mode for curves.