Hi,
First of all, congratullations for this beautiful program. I've purchased it just a couple of days ago and I'm astonished.
I'm a flightsim enthusiast and a developer for X-Plane FS, and needless to say that outerra terrain and lighting are far more realistic than MFS or X-Plane's. I think that with not too much developement a VFR flightsim (focused on light and simple aircrafts) could developed from outerra. I know I'm not saying anything new...
Besides, another thing that I like about outerra is the idea of seeing the world without anything human or before it was infected by this skin disease called mankind or as it was seen by the first humans,... you name it.
With that in mind, how about a prehistoric game? No cities, no roads,... not that much to add (just some flora and fauna: the more, the better). But, in essence, the main things are there already: you have to survive, you have to fight, you have to move, you have to learn some abilities, and so on... The more accurate, the better (i. e., it would be cool to make silex tools following the levallois technique
. A game like skyrim, but without all that "lord of the rings" bullshit (that I love) and 20000 years ago, for example. Something like "Quest for Fire", with that encounter between neanderthals and sapiens...
Just some rough ideas