As I understood the matter, you hit it right on the head with setting a theme for an issue. Not everything needs to be related to the theme, but as long as that theme stands out in most of the work, it would feel unified.
I suspect there might be another meaning behind it, though: Finding an area of design space that is not already oversaturated by other products. Personally, I think that a guidebook to content creation is a very nice niche to fill. There are plenty of system-specific zines producing "crunchy bits," but good resources for world creation are a bit less common.
So it's my opinion that the zine is hitting a segment of the market that will welcome and value it. So long as word gets around that it's available, at any rate!