Looking ito it, as nice a it looks, for a real aircraft simulator it is not that great.
Unigine, same as Ureal or Crytek engine, is depicting "flat world levels". They are pretty, but the are not the basis for playpens the size of what we have now in BoS. They are great for benchmarking, for visualizing construction etc. But for a true sim you need a renderer that can handle a globe based on the world geodetic system, consistent to what is used today in navigation and cartography.
Else, there will be never long distance flights and the flight endurance of a Bf-109G or Yak-3 perfecty acceptable for all purposes.
New game engines, such as unigine, show clearly what you can do when you use modern software interfaces as well as 64 bit software using systems with lots of memory. You can indeed load textures MUCH faster than it is done in ancient FSX. But that is about it. So, like in GTA, you have pretty gass and flowers, houses, all hand placed in a flat playpen. Great to shoot up each other, be it in a Yak or with a shotgun. But not great if you want to fly from East Anglia to Algeria. Flat eathers also have a rotten kind of navigation. If you look at the webpage of unigene, you can see what they do well. An environment for an aircraft simulator, that is like if they put it as "We can do that too! Look at the grass, look at the flowers!" Well, what about a great-circle?
What it also demonstrates is how much more you can deliver if you have a much larger market to draw money from to for investing in a "world renderer" than 777 has. This is why I said it is a burden if developement of the game engine is coupled to the game itself.
And again: pretty graphics have NOTHING to do with a "great flight model". In fact, Unigine has none of that at all. All you can do is move your camera in a world such as you can do in Google Earth. If you would require flight models, you had to tuck it on yourself.