I am sure i saw a screenshot that made it look like the cities would be open
yah, here it is:http://yourimg.in/j/x82z7e.jpg
Not sure that is one of the 5 "massive" cities though.
However I must say I am not too bothered about whether or not cities are open or not, the only thing it really effected was levitation (correct me if I am wrong) which I felt was rather cheap, I would much rather see more interesting and creative ways to access areas that are inaccessable, such as using a crates as a boost or using a plank to make a temporary bridge and while I highly doubt that such a tool would be featured in game I would absolutely love to see grappling hooks.
Of course since the towns and world will presumably be subject to the limitations of a fully open world regardless it would be nice to see cities that are open and a part of the world space however it really isnt too big a deal for me.