We'll hold the Spring GameJam soon enough (in a month or so, starting today, 3 March 2014). Drop all of your ideas for the new GameJam as answers here. Based on a combination of votes and relevance of comments under each answer, we'll make a list of stuff and then a poll, for everyone to vote to choose the final direction the jam will take.
The old jam format (poll to choose themes and so on) will be used as a fallback solution.
Right now, in order to participate, users need reputation. This requires new users to build up some rep if they want to participate. Advertising the jam is a great idea to gain new users, but if the rep requirement will immediately throw them off, we'll not be getting anywhere.
My suggestion: we host the jam externally. We do the submissions and voting there. This way, anyone can participate, regardless of the reputation they have here. Unless there are better options, I could host the jam myself.
I'd like to see as many and as nice games as possible; I think that's the best to get out of a jam. I was thinking that allowing the participants to decide what their games should be about is the best way to achieve this. Removing the specific theme will indeed nullify the imagination exercise, but in turn it will allow people to come up with a great idea themselves, which may be better than anything pertaining to the theme.
So, the next theme should be: "Let's make a game."
I'm very iffy about installing programs on my computer and I think this gives browser-based games an unfair advantage. (The only game I played from the previous game-jam was John's)
To counter this advantage, I would like to propose that submissions must include a short gameplay video.
