That seems to be a trait of you RoR people - insisting on comparing a vehicle simulator with a graphics engine.
So again.
Outerra is a specialized terrain and graphics engine. Specialized in that it does planets and provides procedurally generated world, not an empty level to start with. Any physics you see there is for demo purposes, and no physics goes too deep because that's not the point. The point is the planet and procedural terrain - the very thing you have been attracted by.
Now the soft-body physics can be of course implemented in Outerra, either as a core functionality or as a plugin. But in no way it should be the sole option for physics - not nearly everybody wants it or needs it. Since the engine is in development and none of our customers want such physics, it's not our priority to implement it or to get someone that would do it now. Otherwise we would have done it already, a modern implementation on GPU, which is AFAIK still not available in RoR.
As I've said elsewhere, someday we'd like to make a simulator platform that would be providing terrain and rendering and will allow making plugins with simulator functionality. That way RoR developers could come and make a RoR-style physics plugin, attachable to given vehicles so that RoR people could drive around and delight over flex-whatever, while at the same time somebody flies over in an aircraft controlled by a specialized fine tuned flight dynamics model implemented in another plugin, from a technique he is praying to.
Because never will be all people content with a single physics model, and I assert this is true even if there was a real-life™ model implementation.