A lot of noise about this now.
Also this apparently from one of the better sources for Dortmund
According to information of this editorial an agreement between the clubs is imminent. Borussia Dortmund’s “head of professional football” and long-time chief scout, discoverer of players like Shinji Kagawa or Raphael Guerreiro, will cancel his tents in Dortmund. The new challenge lures, certainly a much more generous salary. To get him out of his current contract will cost Arsenal a hefty fee. According to our information, it is 1.5 million euros.