They should do something to reassure the people that are scared by the "second half of the game" goes linear. Because i think many fears it will become something like The Last of Us (only focused on main content), while i'm pretty sure it will be closer to The Witcher 2 (smaller sectioned areas that you're still able to explore freely, with side content in them), just with the pacing getting much quicker to augment the feel pf urgency, and then it will become liner TLOU style just in the last hours, but with a special way (already shown at PGW) to gl back and explore everything again.
As for the train thing it's pretty obvious it will start from Altissia and take us to Tenebrae and Niflheim's regions, where as i said you'll still be able to roam around a bit, and maybe some smaller areas in between them (Terraverde, the Molborlo area shown last year etc.), and i still think we'll be able to visit the previous one freely by hopping on the train and choosing the destination.
As for the train thing it's pretty obvious it will start from Altissia and take us to Tenebrae and Niflheim's regions, where as i said you'll still be able to roam around a bit, and maybe some smaller areas in between them (Terraverde, the Molborlo area shown last year etc.), and i still think we'll be able to visit the previous one freely by hopping on the train and choosing the destination.