Xhaka show every weeks in Bundesliga that he is a futur WC player , he's only 23 years old , considered already as one of the best midfield in Bundesliga.
Bayern want him.
He's not better than Isco AT THE MOMENT but he would fit perfectly in a midfield trio with Marchisio and Pogba , as he can play like i say as a 6 , 8 or 10...
Isco he still not a starter in Madrid , he still cant take over Bale's place and hes well known for slowing down too much the gamestyle of Real Madrid , he also DONT KNOW HOW TO DEFEND , and when you are a midfielder playing for Juventus Turin the first thing you need to know is to defend.
Xhaka would fit better than Isco in a 3-5-2 or 4-3-3 , is good at attacking AND defending , more promising than Isco who hasnt really improved since some time, and like i say already if Juve dont get him he will probably join Bayern next season after Alonso and then everyone will see how good he is.