I think the issue wasn't so much that it was impossible, but that it would take more resources and time than was practical. It'll be interesting to see what the process for Versus XIII ends up being. Apparently it's going to be super open, and there'll be a world map, but it appears to be in a more modern urban setting, even using real areas of Shibuya as a model. It's been in development since FFXII was halfway done, I think.