I'm on PS4, last I heard that any DLC would be out for that system one month after the exclusives. I really hope they change it, a month is a really long time, but I know it's not unprecedented. I'm guessing due to their track record it's a stand alone quest that can be done any time during the game pre-final mission.
If it is a month, that just seems like bad business to me. It's not going to make anyone buy an Xbox One of better PC (or maybe like 2 people). And on the downside, people who will wait on the other 3 platforms could probably stand a week of waiting, but a month? There is no way they'll avoid spoilers (or this forum) for a month. They'll probably give in and watch it on youtube. So, depending on the quality of DLC in general and what it gives us more of specifically (romance content, gear etc) people will make the decision to either buy it, or say "Meh, I've seen in on youtube, I'll pass."