As nice as it looks i don't think the Devs have the Manpower and money to be able to make the whole Game like this from scratch and a lot of people would cry that their PC can't handle the game. Some are already complaining although it is welloptimized.
Nice stuff. However, before everybody will start to yell: "Look what a single guy did! You can surely convert Astellia to UE4 easily!" - it doesn't work that way and converting the whole game is incomparable to making just a scene preview as seen on the video.