It seems that the content of the Festive Surprise isn't the only thing that was leaked recently. Last year's Christmas DLC was announced and launched around this time, and with the days to the holiday slowly passing us by, it can be assumed that the announcement and release of 2015's Festive Surprise update is right around the corner.
And if a recently posted image, which seemingly contains the entry terms for a new GTA$ 1 million Snapmatic contest focusing on new content which will be released with the Holiday DLC, is to be believed, the new update might be released as soon as later today.

We might be hours away from the joint announcement and launch of the Christmas GTA Online DLC, and not even know it. Based on what is written in the document, the Snapmatic contest itself will begin at 12:01 a.m. ET, meaning Eastern Time, the local time in New York City, so time to set your alarms in relation!
This would suggest that the new update goes live at 12:00 a.m. ET, as one of the requirements for a photo to be eligible is for it to feature content from the DLC itself.