Create a mindmup structures that link to a url for an online outliner (Dynalist etc.) so any change in one is reflected in the other.
So if I have a dynalist node url I can past it as a "linked mindmap node" or some such. They sync to each other so that as I edit one - the other reflects these chances. You see a similar dynamic with some mindmap softwares where a built-in outliner style version of the mindmap exists in a side pannel so that people can create mindmaps easilly and also visualize mindmaps they have made in an outline form just for versatility and adding dynamic ways of visualization and input. This would go a step further and allow people to bring their own favorite outline software creating a synergy between the two - like the synergy that happens when you made MindMup able to integrate with Google Drive.