My team is thinking on focussing the Jam on one particular issue or project. Is that cool?
Every Jam should be open for any ideas under the overarching theme "sustainability". Remember, "Do not bring ... an idea. These will form at the Jam."
So if someone is interested in a particular issue or project, they should go to a Jam, combine their interest with the Secret Theme to make an amazing new idea, pitch it, and hope a team forms. Or they should join a Team addressing a similar issue. Or they should shrug their shoulders and join something completely different which is also cool in some way.
A Jam which is set up to specifically address a certain issue or project, or which is set up by a group who specifically want to work together, is not truly open to all people and all ideas, so it breaks the rule above. It's a mighty, wonderful and cool thing in itself, but it's a workgroup, not a Jam. Do it the weekend after. :)
To follow the music metaphor, going along to an open stage with a your musician friends and a decision to only play Stones songs is not jamming, it's a public rehearsal.
So, no themed Jams please.