I guess if it would be possible, everyone would which a real world size or bigger with 1st , 3rd person and top down view, all kinds of travel options like cars and planes and spaceships, every kind of weapon ever made, packet with quest and poi, to have areas to play rpg and shooter and medevil knight going full melee and building atlantis under the see and the moon reaching tower on the northpole while you can craft,farm,build,become ervything and anything you can think of. Yeah never gonna happen that way....
As much i like huge open world maps, they need to be filled with stuff to do and to explore. The one part says i wanna have more widespread settelments and therefore can better farm herbs and go hunt etc. others would like a ton more raiders and other stuff to kill, while the next one just want a huge free area to build the settelment of their dreams. Anykind of transportation was never really a part of the fallout series and hope it stays that way.
Only if they make a map in real skale to the real world, then i would say ok. But for now we have to live with the game as it is and if they make it bigger it more likly will become a random generatet world and not so nice build up as it is. And i bet that if this would happen, people would complain about that. There was never a game and never will be to make everyone happy without complaining about that or that feature. to make it more challening they could make the enemys strengh and ai more depending to the players lvl and certain areas to start allrdy with a way higher lvl enemy spawn so you have to lvl up.