I've done a bit of research and the OuTerra engine apparently is not an option for Aerosoft's FS, according to a discussion at their forums.
After that, I've checked the current state of FlightGear and dang, I liked what I saw!
It now has an urban shader which basically simulates houses or at least adds a 3D effect to cities and the countryside, very good looking volumetric clouds and a centralized scenery server which provides *everyone* with *all* scenery add-ons uploaded there. Furtermore, you can apparently convert MSFS sceneries and aircraft. The AI system is quite sophisticated, allowing airline traffic, formation flying and aerial refueling.
In the works is a localized weather system, a combat module (A/A, A/G !!) and tons of aircraft.
This sounds awfully good.
Granted, it's not enough to win me over yet, but as soon as I'll get halfway working ATC, a better UI, bug-free AI and more accurate terrain count me in!
Or maybe I should start digging into its programming language right now? Hmm...
FG