I have thought that Sci-Fi / speculative fiction stories are in a really good position to be categorised by something similar to Aarne–Thompson–Uther index.

Consider some basic stories like:

* a person travels backwards through time to prevent a tragedy.

  - By doing so they cause the tragedy to occur.

  - On returning to their own time they discover the tragedy was necessary for their society.

* a person travels backwards in time to meet their hero.

  - they discover the person didn’t exist and become them.
 
  - they discover the person isn’t as heroic as they hoped and coach them.

Just four examples, but I’m sure you can see how many stories fit into each.