CiviDiscount that is dependent on status as of event date?
Figured it out by manually editing the database and seeing how it was represented in the CiviCRM UI, so here's a guide in case anyone has the same need as me:

In order to automatically apply a discount if the contact has a membership that is active as of a specified date (example is February 18, 2017):

In the specify api string for advanced filter box, type {"end_date":{"\u003E":"2017-02-17"}}