The documents mode are a tree based data structure. A graph based data structure is more powerful to express task dependency. Even we use some plugin like org-edna/org-depend to express a dependant task of a headline h1 who isn't a descendant of h1, all functions on subtask can run only for descendant of a headline.

For instance, what will happen if 2 projects p1 and p2 depend a same task t1. t1 is a descendant of p1. And we want know the progress of p2, the progress of t1 won't be integrated to calculation of progress of p2.

To solve this problem, org mode should integrate the notion of symbolic link headline, like in tree based file system, we have file and symlink into a file. I don't think org mode will evolve into this direction, because it is designed to write documents. A document don't need this feature.

What do you think about this limit of org mode to become the ideal task management? How you bypass the problem?

I think to switch into a graph based task management system. Someone know a good open source graph based task management system? If possible like emacs, is fully customizable.