Honestly I don't think it would be that much bigger (bigger yes, but not THAT much.)
Or well, the saves would be about the same size, the engine would be closer to Skyrim or other similar games in terms of size, so that would be obviously a lot bigger, but not really bigger than Skyrim already is, since, the world generation mechanics are not actually all that large.
Keep in mind nearly everything in DF is procedurally generated. You could make an engine to turn the exiting maps into terrain maps, then add rocks and trees and everything more or less like it already does, and generate most of it on the fly with a fixed seed and data in the existing world file.
Honestly I don't think there's anything stopping games like Skyrim from being this complex (I mean, see Daggerfall for comparison), they just choose not to be because they need a friendly learning curve and mass appeal to get the money they spent on making the game back.