TL;DR: In graph view, add ability to links to existing nodes differently from links to non-existing nodes. Currently you can style the nodes differently but not the links.
Obsidian 0.9.0 added
.graph-view.color-fill-unresolved for styling non-existing note nodes in graph view. This is really helpful to distinguish existing from non-existing nodes by styling them differently.
However, it is still difficult to visually distinguish existing vs. non-existing parts of the network when all link-lines are the same color, particularly in dense areas of the graph.
This is a request to add a new CSS class
.color-line-unresolved (or other appropriate name) to style link-lines pointing to non-existing nodes.