What about letting players re-visit previous living story events by buying consumable story books in the gem store (kind of like the Bonus Mission Pack storybooks in GW1). Thus allowing players that are just joining the game, or that were to busy in real life to get on when they were occurring, or maybe just for fun, to go back and “re-live” the events of the past.
I myself got ridiculously busy near the end of the Super Adventure Box and continued to be busy until today, causing me to not finish the Adventure Box achievements and completely missed the last phase of Flame and Frost.