Looks pretty nice at first glance. Only thing I can think of is just the same issues that exist related to Many-to-many relationships should be usable for levels in lists. It works cleanly in that example, but teams might have a very different structure used for project management that won’t be easily presented with these limitations. It seems like this approach breaks down any time there is a shared level somewhere along the lines.
For example, what if I have a common set of concerns across projects that we always want to organize the projects by, which is a pattern we have used in the past using Roadmunk. This could be something like Design, Engineering, Marketing, Testing, and Analysis. For each project, you might want to organize the tasks associated with these common types of activities. Or, you might want to start with these activities, then show the projects, then the tasks. The strict hierarchical nature of this feature greatly limits flexibility and adds a lot of modeling overhead to try to work around.
I’d also like to see Improve Timeline Readability addressed at some point, but I understand this is a more focused feature. At the moment there is such limited ability to display real-world data effectively that it doesn’t matter if there is hierarchy or not.