Is there a way to add non indexed fields to a search api view? I’m wondering if it’s possible to add non-indexed fields to a search API indexed view?

I want the standard flags fields to be available on the indexed search view. And I was thinking I could do this with relationships but nothing shows up as an option.

EDIT: I was using a taxonomy view until my needs required a more robust filtering system, hence the switch to search API. With facets, it gives me robust filtering options so I can segment my content better than taxonomy alone. 

I am building a flashcard website and using Views to display the flashcards and Flags to allow users to mark the flashcards as complete once they memorize the card. This way it can be removed from the main view depending on the status of the flag. So if it isn't flagged it's in the flashcard View, and if they flag it, then it gets removed from the view and I have an attached view, where it will then be listed as memorized. 

I will need all of the standard Flags Views integration options to replicate what I was doing before with my taxonomy view. Otherwise, I will have to patch the Flags module or find an alternative to flags.
If you were using Drupal 7 and Apache Solr, you could get something like this with the Apache Solr Display module:

https://www.drupal.org/project/apachesolr_display

The advantage here is that you can store rendered entity or entity json encoded object inside the Solr index, which allows you to access non-indexed fields. Otherwise you would need to load the node to access those fields.

I'm not sure if there is any analogous module for Drupal 8, but a similar approach might work.