Who would like to have a future feature episode that focuses on either on just before you entered Starfleet/the kdf/arrived on virinat, or see how the Klingon anti-undine campaign started in a holoprogram.
A flashback episode would be amazing but would need a framing character like Q to actually experience this flashback.
My idea for a flashback would be that you are sent back to relive a time aboard your ship maybe that you are an acting ensign aboard your "starting" ship and there is orders for your ship to attack a Klingon fleet in federation space and on the day you are promoted to a full ensign your close friend is murdered and there could be an expansive story where you could take a shuttle or something to take revenge.
This is also usable for Klingon's as revenge is a required part of their culture
However, most of the RP'ers would probable not be so much of a fan, since they have already created back-stories for their chars, and such a mission would without a doubt be contradictory to what they've written.
In that case, how's this sound, we have Q send us to when some of the other races (Klingon, Andorian, Romulan, etc.) first did their warp flights, plus the post flight first contacts that happened as a result.