(Sorry OP, I'm not trying to answer your question, I'm just babbling on about my opinions on maps )
I love traversing large maps. Sometimes, I just want to cruise in my car, driving a normal speed, taking in the sights, listening to the radio. I find that sh*t relaxing. I also love the sense of scale and size. Like when I'm "settled" in one section of map and missions are local then I need to go to another city or destination, the first time I go there, I'll take the long, arduous journey there for the same of realism and feel small in a big map/universe.
Unfortunately, the massive maps lack detail like a IV's Liberty City or Watch Dogs 2's San Francisco can offer. My dream is to have the large scale map like Just Cause 2's with the detail of a Deus Ex map or the detail of a Watch Dog's map. At least two cities, separated by large and mountains land mass, diverse environments from desert to lush green and wooded mountains with lakes and rivers with little towns contrasted with a Watch-Dogs size city, large skyscrapers, full of people, cars, and things moving. That might not happen for a time yet but I think we're getting closer.
For me, city-size like Los Santos in V or Liberty City in IV is the perfect size. I don't think cities need to go any bigger than them, really. Maybe it's because my city is small, but I think in the context of a video game, Los Santos, San Fran in WD2 or Liberty in IV is sizable enough that it encompasses everything a city should have in a game. Also walking across it will take quite some time and frankly would a little boring at the current size of cities and I don't think making them better will add much more value. Perhaps a little bigger to appear more realistic. But traveling from one side of the city is just OK at the current sizes. If the cities remain this size for the next few titles in GTA or Watch Dogs, I'll be happy. Just make the cities more detailed, more explorable, more enterable sewers, buildings, malls etc etc.
Although I love a huge map, I miss the detail. So playing Watch Dogs 2, the map isn't massive but it doesn't feel small. There's always something going on. It's highly detailed.