Makes sense for both parties.
Bayern need a Ribery replacement and De Bruyne can play there quite well afaik.
Douglas Costa and KDB will help Bayern remain effective after Robbery although Robbery in their prime can never be replaced.
Besides KDB already tried BPL and maybe he felt that the league just doesn't suit him.
I'm not so sure about that.
As I see it KDB doesn't have Pep's usual wide attacker profile at all. He's really not the lightening fast tight space dribbler that he usually sticks on the wings. He's much more of a traditional CAM, who of course also can play wide, who thrives on being allowed to roam more freely, and as far as I know, the current Bayern system just doesn't have room for one of type. If they are indeed after him, I'm sure Pep has plans to fit him in somewhere, but I can't see him being a 1 for 1 Ribery heir at all, and not letting him to play to his obvious strengths would be borderline criminal after his brilliant 14/15 season.
Then again, it would make perfect sense according to Bayern's transfer policy of buying up the stars of their Bundesliga rivals.