Going to make a guess here and say that Leon's scenario takes place before RE5 with Chris and new guy's scenarios happening concurrently a few years later.
Capcom Press Release said:
It has been ten years since the Raccoon City incident and the President of the United States has decided to reveal the truth behind what took place in the belief that it will curb the current resurgence in bioterrorist activity. Due to be by the Presidents side is his personal friend and Raccoon City survivor, Leon S. Kennedy, but when the venue suffers a bioterrorist attack, Leon is forced to face a President transformed beyond recognition and make his hardest ever decision. At the same time, Bioterrorism Security Assessment Alliance member Chris Redfield arrives in China, itself under threat of a bioterrorist attack. With no country safe from these attacks and the ensuing outbreaks, the entire worlds population is united by a common fear that there is no hope left.
If I am reading that right, that should eliminate your theory, but I do hope this is a sequel to Resident Evil 5, and not a prequel.
The third secret playable character could have the "sequel" storyline to Resident Evil 5, while Leon and Chris have the prequel storyline if this talk about it being a prequel to RE5 holds true.
I noticed that Leon's story seems to have zombies, while Chris's story has something similar to the Uroboros enemies, could this mean there would be two different antagonist groups/individual at work here?
Isn't Uroboros suppose to be more powerful since it was a combination of all the different viruses from RE4 and before it? Doesn't make sense to unleash a inferior virus if you have access to a more powerful one.
This was definitely a great trailer, and loved that it was more than 3 minutes, and provided plenty of juicy material for fans to theorize and play with while we wait until November. I was expecting any kind of announcement of Resident Evil 6 to follow with some sort of 30 second teaser with a few flashes of cut scenes and a logo than a Spring or Fall 2013 release date at the end of the trailer, but it far exceeded my expectations with the length of the trailer, and a November 2012 release date.