It seems that there is no module in the contribution repository which simulates the behaviour like this of terms in given vocabulary or menu items in a given menu from system modules in Drupal 7. (?) Wouldn't it be an interesting use-case to achieve something like entity trees simultaniously this way, like a task and sub task management, with a given weight and relation to each other to build parent and subordinary relations between them? I know about many reference and relation modules and asked already some specific questions about them and their limits here but I can't find an entry point where I could start to contribute on this special scenario. I can easely drag and drop taxonomy terms or menu items and give them an "order" and sub "order" in their hierarchy already from core and the system "knows" about this order. Not only of one level, also for more levels. It is not visually only. So I can build paths based on that relations. It seems that this is not possible to make with entities and any reference or relation modules out there ? Am I right or is my question asked the wrong way around?