We already can do the terrain, no one now really builds terrains for AH3 trying to do the real world other than AvA and special events. You can see that EU winter arena is repeating tiles like ours, they look more like 2x2 to conceal the visual repetition of painting large areas with the same tile. Probably even SpeedTree trees and clutter. But, we cannot do the objects because our arena is vastly larger and would kill FPS. One of their arenas would fit into one of our sectors, so they can stuff in objects and not kill FPS with what, 16 or less per side for each timed match up. I can do the clouds if everyone wants to fly around with an FPS of 12-27. I recently did weather systems for our MA terrains and had to keep cloud blocks separated by 40 miles to not impact FPS. Those water drop objects would impact FPS in our giant arenas. Land area painted with trees, bushes, grass and houses adds up to a LARGE number of static objects for every 40 miles of view distance. Then throw in moving airplanes, vehicles, clouds. If you have the equivalent of one of our sectors filled with static objects, then that's 10-20x less objects than we have. So yes you can have eye candy to make your eyes bleed but, with 32 people per arena.
It looks like an IL2 x,y or z version game video which shows the linage of the WT product creators. If we stuff 100-200 players into one of our sectors in a fight, many people suffer the slide show effect. Back when we could get 60 bombers with up to 20 escorts, diving into that reduced just about everyone to a slide show. During the last FSO, the allies upped a large bomber force with fighters, diving through it was a slide show for a few moments. It was also a white knuckle experience for all participants not soon forgotten.
Comes down to trade offs, whether to have a giant open world with more than 32 players flying, driving and sailing around 24x7 together. Or eye candy bleed with 32 players limited to flying or driving in separate ride type arenas on a session timer.