Spaced repetition as soft alarm clock
Typical alarm clocks are hard in the sense that they require precisely choosing some future moment in time at which to sound the alarm. Some alarms have a "snooze" button, but these snoozes come at fixed intervals. Spaced repetition systems can act as soft alarm clocks; you communicate basically "just leave me alone for a while", and each time you say that, the "alarm clock" leaves you alone for longer and longer periods of time. This can be useful for speculative projects in a to-do list (i.e. where you don't need to do these tasks, but they're sort of like "I'm kinda excited about doing this some day").
This is analogous to the distinction between traditional programming and machine learning.