This maybe a request fairly specific to my company's user case and would likely only come after custom field calculations are released.
It would be beneficial to be able to specify that a task's, project's or subtask's custom field value could be inherited from it's parent location (tasks/project).
Specifically if some users are only shared into a task and not the parent folder/project then it might be beneficial to have the same values in custom fields (if these were used to inform the assignee regarding the task). However having to duplicate changes throughout all the tasks in a project (if a change occurs) would potentially be quite a substantial job.
I hope that made some degree of sense, thank you for taking the time to read this,