Interesting idea about not immediately removing text upon unlinking. You may be interested in this somewhat similar request I made: Mermaid with Obsidian capabilities. I guess it could be just as well applied to the Mindmap plugin. Not sure how feasible either are, but I am definitely with you that there is a lot of potential for experimentation.
With the easy linking capabilities that Obsidian already offers, I kind of always dreamed of it being part of the native graph view and imagine various ways to view connections, like here: Hybrid Graph View - Local Mode
Thanks.