I believe i am late to the party but let us wake the slumbering beast once more. I got curious about the engine and pikkoserver. It seems pikkoserver runs only in unity and is not integrated into other engines yet, unreal is an ongoing thing which is stated on their site. View: https://www.youtube.com/watch?v=5nirX_4c0Kk 1 year old. a few months ago from now unity engine has achieved some insane photorealism graphics truly cool, but the video has normal nudity to showcase so i can not link it here, just search in google "unity photorealism", it will pop up or in youtube. If behaviour is using the newest stuff and really are milking the unity for all its worth, eternal crusade will look splendid, but unity or nothing at this point.
If your trying to ask what games have been made on the Unity engine, Starforge comes to mind. Starforge is pushing everything the Unity engine can do.
I think DEVs have already decided what engine to use, since their pre-alpha game is already running on something. I guess we'll find out soon enough I'm not so optimistic about Unity engine though (if they decided to use it), since I know quite a few games that run it - they are usually small "cartooney", "plastic-looking" indie-games. But who knows, maybe Unity has something up it's sleeve to amaze us with. Only a DEV would know the boundaries and possibilities of the game engine Anyway, I'm sure they made a right decision in the end