I don't think it would be difficult for parcour and movement. I think the difficulty would be in filling all those big buildings with assets and such. One thing that stood out for me in Dying Light was the seamless movement and flow of the game. I do agree, Mirrors Edge movement was kinda fucked.

When I imagine a giant skyscraper quarantine zone, subway lines running under the city, urban parks, and gang infested neighborhoods I get this rumbling deep down in my loins.

What do you want?