I think Maxis will be announcing the next gamepack very soon. I'm hoping it will be next week.
What do I base my theory on?
Cause the February Patch is being released on a Thursday and Patches released on Thursday are generally Pre Stuffpack and Gamepack. Normal patches just release on Tuesday. I don't think they'd already be hyping the Feb 25th Patch if this wasn't a Pre Gamepack Patch. I don't think the 21st annivesary is big enough to hype this far out in advance and even if it was it would most likely come on Tuesday.
Now I'm hoping the Gamepack Announcement will be announced Next Week or the Week after. If it's next week I hope we get a Teaser on Monday but keep in mind sometimes Teasers come on Tuesday and Trailers release on Wednesdays.
Also some people are saying we just got a Stuffpack. True but they've released Stuffpacks and Gamepacks in the same month before.