Thanks for your response. I was about to reply myself because I watched TLG announcement video that stated there is not going to be a theme.
I disagree with a themeless jam. Constraint is the nature of a jam--it's in the name. Having a Linux build is hardly a constraint these days. Something like a theme, size limit, or limited subject matter (eg 'Public Domain Jam') is very helpful. It also unifies the people and the projects of a jam.