He's already done alot for Manchester City, I really do think it's time for him to part ways with Manchester City. Barcelona have been linked already, and how they play really suits him as he will not find it difficult to adapt to Barcelona.
As for Manchester City, they already have the England forward Kalvin Philips, still making advanaces to Introduce Kovacic from Chelsea.
I really do think it'll be a done deal because Mauricio Pochetino has plans to recruit his own players especially for the midfielder's.
He's finally won the Champions League, now he can explore but no Saudi Arabian club wants him currently.
Maybe it's true as you said that Gundogan has got it all with manchester city and he will look at the future with new challenges with other teams in the next season. Barcelona are even very interested in getting Gundogan, but for now Gundogan has not provided any clarity regarding his future even for now I don't think he will think about it because he is on vacation after helping Manchester City win the Trophy UCL.
I feel that his impressive performance with Manchester City this season will spark the interest of several big teams to get him, especially at the end of this month he will clearly have his status as a free transfer player which will make a number of big European clubs try to approach him.