I think the ability to mod shouldn't be considered. I mean, you buy the game first for the experience it brings and not a modder playground. Oblivion was a perfect modder playground but it ended up to suffer a great deal for it, why bother making huge spaces if you leave most of it empty for modders? I have nothing against modders, but the biggest issue should be about trying to optimize everything for vanilla gamers, the "canon" experience. If you need dozens of mods to make the place feel more alive and less empty, there's a problem, making a game isn't a cooperation between developers and modders. Plus, it didn't disable people from modding extensively Morrowind. Having said that, the moment I get a new PC, I get Oblivion and download loads of game fixing mods as well as the Hammerfell thing.
Well, if they're gonna spend time on making a construction set and making the game able to be modded, then I'm sure they are gonna put some attention to what modders will want and need.
Also, I'm sure they get A LOT of inspiration from user made mods :wink_smile:
I do think that Bethesda did rely to heavily on PC modders to fix certain problems in the game, the unofficial patch has a staggering list of fixes.
But however, in saying that, there will always be empty space in sandbox games anyway, because it adds to the feeling of a large world. You wouldn't want dungeons and cities to be shoulder to shoulder with each other. I don't think any empty space is left on purpose, I'm sure it would be the same with modders taken into account or not.