Personally I think there are already far too many themed galleries. I wasn't a great fan of the 'Synchronicity' concept when it was first introduced, and by now it's an idea that is more than a little overworked.
As can be seen by the way that many of the entrants play fast-and-loose with the themes anyway, it's not a particularly serious restriction. So why bother with it? I can see a few special-concept galleries during the year (maybe 3 or 4), with perhaps more (or less) stringent rules on what is done post-exposure. And the occasional concept them _does_ often force you to think outside your normal photographic habits. But we've already lost 50% of the year to themed galleries - that's more than enough. And while I'm sounding off: I'm strongly opposed to "Digital" as a theme. I can capture exposures with film, or with a CCD sensor. I can manipulate the image on my computer, or I can perform all sorts of tricks with cross- processing, dodging, burning, and multiple exposures in the darkroom. The end result should be what is judged, not the means used to get there. Not to mention the fact that having a specific "Digital" gallery rather sends the message that digital images are less welcome in other months.