I think Zelda Wii U could do a number of things to be more 'ambitious' then Xenoblade X.
I am eagerly awaiting both games but from what I have heard XCX's open world while massive, doesn't have a lot of variety in missions, usually it is go to area or kill this creature(s) or talk this guy and kill this creature. It is similar to standard RPGs in that MMORPG or standard action RPG/Hunting game mold.
Zelda Wii U could be more ambitious being similar to other more successful open sandbox world games, giving the player a number of things to do besides monster killing and dungeon crawling like fishing, racing, farming, etc. It could also go something of the route seen Majora's Mask or more recently the Mass Effect series plus the Witcher 3 and have a lot of deep side stories that may or may not lead to one of multiple endings.
'Ambition' is relative, XCX the ambition was to make a massive world with multiplayer components and the Xenoblade battle system. With Zelda Wii U, one would hope given all the hype, they are aiming toward a truly unique Zelda experience that will surpass the classics that came before it and match some of the freedoms other more modern games have provided players.