Chosen Solution
I opened up my MBPr Late 2013 and saw that on both sides, near the fold (where the display folds) there are two similar looking elements. Please see attached image. One of the was loose and after placing it back in its place I no longer have any “no hardware found: wifi” issues. I know the airport card is next to the ram, so it can’t be that. Therefore I wonder what those things are and if they are related to the fix of my wifi problem? Or if it is just sheer coincidence?
Those are rubber hinge covers on the 15" machine. See steps 9 & 10 of this guide: MacBook Pro 15" Retina Display Late 2013 Display Assembly Replacement
