This is something I've always thought would be useful as well, but after seeing some demos of it in action [1], I'm now not so sure. One of the issues I see is that because of the infinite zooming/scaling, there's no sense of place or spatial awareness that you get with a 2D map, or even a traditional outline. I think it would be easy to get lost if you had too much nesting and a lot of content.

Maybe on a smaller scale, it would be manageable though. I remember seeing some presentations that use Prezi and that has the ability to nest text at different zoom levels, and the transitions between slides worked pretty well and you did still have a sense of place, but the presenters didn't have tons of content all over like in the youtube link. I wish I had a link handy for the Prezi presentation I saw online because some of them were structured like your description about different zoom levels, like a fractal.

[1] https://www.youtube.com/watch?v=GblI7GI0jQ4&t=85s