I settled on something very similar. I split between tasks and goals, and I subdivide tasks into to-do and backlog. For example, "Implement a TSP solver in JS"

I settled on something very similar. I split between tasks and goals, and I subdivide tasks into to-do and backlog. For example, "Implement a TSP solver in JS" is a task. "Learn JS" is a goal. I'm very ok with the backlog being where good ideas go to die, and I'm very ok with sub-tasks (indented list).