Bunch of people played it now.
Maximilliandood is one of them. He made a video a few days ago about the size of the map.
He said that a lot of people are worried/believe that the world map will be like the later FF titles. More like zones, and not really a large map.
A minute into the video he talks about a quote from Hamaguchi
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Question
Speaking of that world map and that expanded play space, is that something that's all interconnected or is it more of a world map system where you can travel to different regions at any time?
Answer
That's a great question, that's something I really wanted people to ask me. What we've done is we've taken the world map from the original Final Fantasy VII, but we've created it all in a one-to-one real scale. So all of the dungeons, all of the cities, everything in that world is now included in the same space. One seamless map.
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He goes on to say that they expanded on that saying that you can go from one end of the map to the other. Like crossing the ocean.
From what it seems the demo they played was sectioned off similarly to the network tests for Elden Ring.
Max then shows the world map and explains demo size that was playable, and compares it to the map he had access to. (3ish minutes into the video)
If it is accurate. This game is ridiculously big.
EDIT: Watching more of the video now. He tries measuring things with quests markers and such based on videos. Then there is a quote he found where Midgar is supposed to be 6km in width. For comparison, Horizon Forbidden west is 7.7km at its widest. Which seems wild, but then there are quest markers from the trailers at 11km away.