Hey there...
i just fell in love with your Techdemo!
The first thing, that came to my mind was "Hey, a Trial-Simulation with Heavy Trucks an/or Bikes like a GasGas etc. must be great". Another idea i have is a Rally-Game like "Colin McRae Rally" BUT with open terrain. Navigating with maps and GPS to stay on route, using landmarks for reference...
Man, im dreaming about such a game for many years.
Flight Simulation is a hard thing to master, i guess.
DCS ist doing very well in this sector, im looking forward for the new "A-10 C"!
Dont waste your engine for a casual game. Do something special with it.
What about a Heli-Simulation like "Air-Rescue"?
That game was great, but the simulation itself was solala. The landscape-engine was horrible (like my english)
There are plenty of Missions possible (burning Oil rig, Hikers lost in Mountains, Traffic accident, supporting Police...).
A Tank-Simulation like "M1 Tank Platoon"
"Apache Longbow II"
All these ideas dont require much Story. So u can concentrate on the technical aspects.
If u need Brainpower to flesh out some ideas, there are plenty of ppl in this forum to help u out.