The precedent would be set should the Germans move the venue of Brueckner's trial on the residency issue. I think it may actually have been a consideration when he was constituted arguido.
Portugal would have apply to Italy for the right to extradite Brueckner for the purpose of trying him for Madeleine's murder in Portugal. I think Germany would contest that and the case would end up in ECJ - again.
I don't think the venue will be changed in Germany as CB has already been tried & convicted once in Braunschweig court with no objection raised as to the court's authority based on residency. Furthermore, the additional 5 charges were laid by Braunschweig district court last October which was after Fulscher had raised the legal issue.
Finally, I think we would have heard by now, probably via Jon Clarke, that the victims (particularly Hazel) would be facing a further delay in proceedings. Such procedural issues would be sorted out far more quickly in Germany than we are used to seeing in Portugal.