The reason you don't see many videos explaining the creation of such large terrains, is because it's extremely resource intensive to create said terrain. There are a lot of optimization tactics that go into creating a decent open world game. That being said, the outerra engine anteworld demo is probably created with the help of world machine.
1. Yes it can be done 2. Yes there are indeed ways to load the tiles in an intelligent manner, such that they can be rendered at decent frame rates. How can it be done? Start researching online, it's a long and complicated process. 3. To create a believable terrain at that scale, you need to work at a very high level on all levels of the pipeline. You need to master world machine, as well as said engine's level design features. Look at stuff on Epic's "Kite world demo", look at how it was created and what challenges they faced.
This is a big challenge, even for a mid range studio. Good luck with your project!
for my project I need to create really large model of alternative world that is approximately as large as 1000x1000 km. Think of it as tiny version of Outtera. I know that world machine works with tiles and it is possible to work within smaller tiles because such large world cannot be rendered at once. But I could not find any videos that would cover such large worlds to see the workflow and to see wether it can realy deliver what I need. Then I would like to transfer the terrain to Unity or Unreal and work on it a bit more, but are these engines able to work with those tiles from World Machine and render them procedurally on a scale of 1000x1000 km in reasonable resolution? I mean am I going to be able to fly through the whole world with some procedural rendering or is it always goint to be limited to one or few tiles that can be reviewed? I am asking this question becasue I never saw anyone building this large scenes using World Machine and then sending it to Unity or Unreal.
Does any of you have experience with building such large worlds or knows any project that was build that way in World Machine? Or do you at least understand my request and can you assure me that what I need is possible with World Machine and Unity or Unreal?