Evolution in the scope of the site is not a bad thing, we've learned a lot about what does and does not work in the over-a-year since the site first entered private beta. I'll use a number of my own questions as examples here to avoid picking on anyone else.
Certain questions are clearly both popular and answerable both from the number of views and the number of up-votes they are getting. I've chosen my top 5 highest voted questions to discuss. Of the 48 questions I've asked at the time of writing these are the five that proved the most popular with voters. It's notable that each of these was also on the Hot Network Question list and in at least one case was on it for over a week. As a result many of the people voting may well not have been regular Worldbuilding users, however regular Worldbuilders did get it into HNQ in the first place.
About Worldbuilding? This is not about defining something concrete and part of the world, for example a mountain or a city. However it is about mechanics inside a world. Specifically what methods are feasible for people to use to face this threat. When designing a mountain part of building that world is specifying how people can climb that mountain. Here I've defined part of the mountain (Cthulu friending people) but am looking for plausible ways to climb it.
Risking off-topic? Borderline on whether it is plot or world building.
About Worldbuilding? This one treads close to the "actions of an individual person" line. The "out" here is that Satan/Santa isn't really treated as an individual character, it's an essential part of the framing of the world.
Risking off-topic? Borderline on "individual person" or Worldbuilding. Note that I wrote this as part of the "Santa" challenge which almost guaranteed a lot of questions about an individual, was that challenge a bad idea? It was certainly popular both with regular users of the site and visitors.
About Worldbuilding? Selecting methods of government for countries is an important part of worldbuilding when working at that scale.
Risking off-topic? It Risks straying into "list based" answers or idea generation which is why I was careful to narrow the field and specify the criteria by which answers would be rated.
About Worldbuilding? This is about building the society of inhabitants of a world. While individual people would be using these terms that actual nature of them is a part of that society and hence the world.
Risking off-topic? This had the same problem as the "post democracy" question that it could easily be too broad or Idea Generation.
About Worldbuilding? This is clearly about building worlds (or multiple worlds).
Risking off-topic? Again this risks going too broad or idea generation.
Hopefully this list starts to illustrate the problem here, every single one of those questions could be argued as either off topic or on topic. Looking at my next few questions we see the same thing as well: Alien Viewpoints risks idea generation, Centaur Feeding is probably fine, Natural Projectile Weapons again could be idea generation, Landmass Formation is fine.
So of my top 9 questions only 2 do not in some way risk being classified as off topic. So where do we draw the line? Is the popularity of these questions enough to justify their existence? My personal opinion is that by itself popularity is not enough to save a single question, however if a lot of similar questions are popular then we should consider the fact that clearly the people using this site have an appetite for questions along these lines.
So I invite people, take a look at these questions and answer in the comments to this answer. Should they be closed, if so why? If not then do we need to adjust the guidelines to say why they should not be closed? I promise not to get offended, I just offered them up as sacrifices for the greater good after all :)
For what it's worth I believe that all those questions are on topic for the site (or I wouldn't have asked them) but several are definitely pushing a long way into the "grey area" between what is actually building the world and what is not. Anything that can reduce the grey and make the boundaries more explicit would be a positive step.