The Rainbox Six: Siege Twitter account posted a picture (included below) that seems to indicate an upcoming DLC, however, no other information was given aside from a caption saying "時は、来たれり", which, if you run it through online translation services, translates to "Time, come Tareri".
We don't know what the caption means or what it signifies, but the fact the writing is in Japanese is most likely significant, meaning we may well see the new DLC in Japan. This would also seem to be confirmed by Twitter user @JonKay20 who tweeted a video showing gameplay in a Japanese setting, a leak which may have given away what Ubisoft were trying to keep so secret.
Would you like to see the DLC in Japan?