Problem: The default plain list and linear mode of management for tasks within a project seems to be sub-optimal. I'm aware of the tree representation of tasks and sub-tasks, but that view is static - a user cannot manage task relations using drag-and-drop (DND)-based UI.
Suggestion: I would suggest considering of a more dynamic DND-based UI for tasks management, at least, within a single project. I'm pretty sure there are arguments pro and contra, but I thought I would start relevant discussion (if similar discussion exists, please point me to it).
Rationale: A DND-based tasks manipulation might improve Phabricator's UX, as such visual manipulation IMHO better fits users' relevant mental model.