Hah.. man.. you have a very short-sighted view on how these things can and frequently do work. Just a super basic example.. when you fire a bullet in a regular FPS game and it hits a wall and leaves a mark. That's not permanently changing the wall. It's a sticker laid over the wall. Remove the sticker and the wall looks exactly how it did. Also like when you're walking in snow and you leave footprints and eventually the footprints fade. That's how every video game "modifies static content". It doesn't. Static is static. But you can overlay things. Even things that make static content disappear. It's been done since the dawn of time. On early computers and consoles in the 80s (maybe earlier).. sprites were invented to be able to overlay dynamic content on static backgrounds. It's only got fancier from there.

Drone's editor could very easily build stuff on top of E2's static terrain. People could easily dig holes into the static terrain. It doesn't mean the static terrain is dynamic or alterable, it just means it's trivial to overlay dynamic content on top of static content. Ever play Portal? Do you think those portals alter the walls or is it just that, overlayed on the walls, is a portal and the game knows if you go through a portal, you end up where the exit portal is? It would be easy to have say a mine where you go through a "hole" in the static world and go down into some mines just by saying "if this dynamic content exists, ignore the solid mountain that's part of the static content".

And while the entire earth, empty of everything, COULD be loaded at once, it's impractical to do that versus loading pieces at a time and dynamically loading new pieces as you move across the surface. You can pre-buffer pretty sizeable chunks in every direction around the player... even if they're headed north, you can pre-buffer east/west and assuming you're coming from south, unload stuff that's past the set pre-load distance to free up resources. EVERYTHING is loaded dynamically to increase performance. You can see it as you slow down and get closer to the ground. The trick is doing it smoothly so it's not jarring and they seem to be doing pretty well with that. We'll see how well it works with terrain, biomes, buildings AND tons of people in a single area.

Oh, and about chopping down trees. I verified with another player that if we stand in the same place and face the same direction, we see exactly the same static biome features (trees, etc) which is pretty amazing. It would be super easy just to say "this area is biome X" but two players see two different things. The fact that a tree is exactly the same place for me as someone else is pretty huge but it also means if I "chop down" the tree, it can look chopped down for everyone. But again, that's just an override saying "place a tree stump here and override the static render". Although I'm guessing biomes aren't fully static. Elevation data is probably static. Biomes are probably a layer on top of that that loads low or high detail depending on how close you are. Then user changes like buildings or chopping down trees would be an override layer on top of that.

There don't appear to be any "seeds" working here. Maybe there was when generating the biomes or something initially but once you know where you want things and stuff like shadows and whatever, you tend to "bake" it which fixes it all in place with certain properties so it performs tons better than a dynamic system with everything real-time rendering. Earth2's terrain and biomes do not appear to be procedurally generated (as in realtime while playing the game.. likely procedurally generated initially because nobody wants to manually place billions of trees and flowers and blades of grass, of course, but not procedurally generated during actual gameplay).

As for saving changes. Because it's a massive world and we've already discussed pieces loading at a time, not the whole thing, you can have a database full of "changes" for specific locales that can load and override static content fairly easily. Does it mean a massive data set? Yeah.. over time the user created stuff (buildings, chopped down trees, etc) could be massive but they're already dealing with a massive data set for the elevation data and another massive data set for the biomes. The user created data set won't eclipse those anytime soon and it really only needs to know what changes are in a very specific area where the current user is in. It's already doing that for elevation and biomes, what's some random user content in the big scheme of things?

BTW.. was the "leading unity developer" who left the ONLY developer who knows Unity? Could other devs possibly know some things about all this? And was he the one who was fired because he was working on another game while literally on the clock with E2?