Epic is working quickly to fix the problem and allay your fears of not being able to play the game you forgot about last week when Battlefield came out. Community Manager Will Kinsler wrote on the forums:
We apologize to those of you who are anxiously awaiting to play. We know this is disappointing news as we’ve seen a lot of posts today showing excitement for this content. We have folks working around the clock to resolve this issue ASAP so you can all play and enjoy the Command Pack.
When it does come out, the DLC will bring new playable characters, maps, weapon skins, and changes to Horde Mode.