Update: Ubisoft has now responded to the trademark abandonment by filing a petition to the United States Patent and Trademark Office saying that the trademark abandonment was a fraudulent filing. Ubisoft would like to see the trademark for Watch Dogs “promptly” revived.
The most likely option is that they are just going to trademark it as something like Watch_Dogs instead, which some of the marketing has done in the past. There is also the possibility of a full rebranding of the name to something different or perhaps that it was a mistake of sorts.
The most unlikely option is that the game has been outright cancelled, which would be insane considering how close it was to release back in the fall. However, gaming can be a weird industry and who knows. At this point, all we can do is wait for Ubisoft to respond.