Velen alone is bigger than all of Skyrim. You'll be able to make your huge treks. Try walking from Novigrad to the Nilfgaardian encampment to the south.
Think of Skellige as Solstheim, if you will. That was in its own seperate zone, too.
The more I play of this game, the more I hope Bethesda takes a long, hard look at it as well. This is the sense of scale and realism I want from TES VI. A huge, varied overworld, dotted with numerous small settlements and a few large cities. Fuck, most of the little towns have the same amount of NPC's as Solitude in Skyrim, and that was the nation's capital. Beth needs to step off the idea that every NPC needs a unique name and a completely unique schedule. I don't need to know the name of every lowly soul tilling the earth. I want crowds. I want cities on the scale of Novigrad.
Just thinking about being able to explore all that in first person makes me giddy. Skyrim's my GOAT, but damn if this one isn't a serious contender. I really hope Bethesda takes note.