It was an exciting possibility, but it's not to be. City of Heroes developer Back Alley Brawler, otherwise known as Christopher Bruce, has provided a series of illuminating posts that explain what's actually going on.
A revamped version of the Winter Event, along with 'other surprises', still remain to be tested for the current Issue before Issue 13 will show up. As far as timing goes, it's possible that Issue 13 may not be ready to go live by the time the Winter Event needs to happen, which is why the events are being tested for the current Issue.
There's an acute sense of something very, very big around the corner in City of Heroes. Many developer posts and comments hint at this, but it's clear nobody can give anything definite away yet. Christopher mentioned in a previous post 'Player created missions is only one of the things you guys have heard about...but there are some other big things also being worked on as well. Things that haven't been announced yet. Chew on that for a while. We've announced player created missions. What do you think we might be working on that we didn't feel comfortable announcing yet?'
He has also said 'You will be getting more information about what's coming in Issue 13 and beyond...just not right now. Information is a very powerful, but short lived resource for us. It's in everyone's best interest to utilize it to its maximum potential by releasing it in the right time and the right place.'
Since Christopher's invited speculation: what do we think they might be working on that they didn't feel comfortable announcing? An Archnemesis system, perhaps, like the one mooted for Champions Online? Environments that respond to player actions, as the Recluse's Victory zone pioneered? The facility for heroes and villains to change sides? The long-requested Moon Zone, or an underwater region, or even vehicles? Whatever it is, if it's on a par with player created missions, the future of City of Heroes looks rock solid, even in the face of increased competition.