Integrating Workflowy, Trello, and mindmaps would produce a better, more useful, and more complete tool.

All three use the same data structure (lists) and present it in three different ways. These three data UIs excel in different ways at input, editing, and output and are most appropriate for different tasks.

A couple of ideas for example: Workflowy is a better way to generate a mindmap, so how about a mindmap that allows you to enter your text in Workflowy style on the left half of the screen and shows you the mindmap on the right side of the screen? How about taking a node in Workflowy and allowing the user to interact with it through a Trello-style UI?

I feel there's a ton of opportunity here in personal thought management that hasn't had a killer UI yet. It's possible to get it just right, but would take an incredible design. Workflowy is the closest I've seen.