Agreed that we're not trying to put together a puzzle, we need some kind of unifying, homogenous idea, but I also fully understand modernhamlet's concern. As of right now, it looks like we're just aiming for "generic"? While that can be easy, shouldn't we be aiming for a challenge? Something unique and interesting?
This is entirely plausible while still remaining within the realm of the mid-fantasy genre. But wouldn't it be more interesting to introduce your friends/rpg players to something that they haven't seen yet? Even in the context of something comfortable and familiar?
I took a couple writing prompts from a website, and I came up with a few ideas. Mull them over.
Prompt --- My idea.
The outsiders --- perhaps this world is being visited by people or creatures from a strange land, a strange planet, a strange universe all together, maybe a strange dimension. How would a mid-fantasy realm react, and what would the repercussions be, to an incursion from something severely outside it's own "norm". What if it were visited by a space-faring race that had lost its own homeworld. How does technology collide with fantasy and magic?
What if they are being visited by beings that once lived on the moon, or if we are working on the moon, then beings from the planet? Even through a magical portal or some dimensional rift, what does the effect of one fantasy world have on the other if two otherwise independent fantasy realms suddenly converged? Or maybe two dimensions have merged into one, and only people with magical talent are able to see the beings from the other dimension, and vice-versa. What happens to a world where a small portion of the population can "see things" that nobody else can, and the majority of people from both dimensions are plagued by the actions and unexplainable terrors of the pull their actions unknowingly have on the other dimension. Does a fire in a firepit in one dimension start a housefire in the other? Is a man standing on a bridge in one dimension seen floating in the sky in the other?
I was here once. --- What if resurrection is a very real part of the life cycle in this world? How does that play out? What are the physical requirements for that to occur and what are the sociological and geopolitical repercussions of that fact? What about the religious effect on geopolitics? Most importantly, how could you prevent it, and what affect on the world would that have?
The guilt that haunts me. --- What if every major deed, good or bad, physically brought a demon of some kind into the world? Every life saved or taken had a physical manifestation brought into being somewhere. Free to interact with the world and help or prey on its targets and form coteries of spirits. How does this world stop them? How does this world still exist? It seems like a problem like this would nearly instantly create an interminable tide of darkness if not for some sort of balance between the good and evil in man. But what about the other races, what if their morality is not so ambiguous, and the invasion of dark spirits is something they aim to attain? And what role do the good spirits play, how do they work to protect the world? What of any religious/political ideas surrounding this problem?
There are ways to do a mid-fantasy world that still allows for a significant amount of "new" and creative ideas that affect both the story and writing side of the world as well as its physical and political manifestations.