The following article contains an answer for the question: What is the name of the person that claimed that the staging is definitive and sacrosanct? , can you please find it? 

The 1951 Festival production, by Siegfried's and Winifred's son Wieland, broke with tradition and featured an austere staging which replaced scenery and props with skilful lighting effects. The Rhinemaidens, along with all the other characters, were plainly dressed in simple robes, and sang their roles without histrionics. Thus the music and the words became the main focus of attention. Wieland was influenced by Adolphe Appia, whose Notes sur l'Anneau du Nibelungen (1924–25) had been dismissed by Cosima: "Appia seems to be unaware that the Ring was performed here in 1876. It follows that the staging is definitive and sacrosanct." However, Wieland and his brother Wolfgang praised Appia: "... the stylised stage, inspired by the music and the realisation of three-dimensional space – constitute the initial impulses for a reform of operatic stagings which led quite logically to the 'New Bayreuth' style."The innovative centenary Bayreuth Ring, directed by Patrice Chéreau, did away altogether with the underwater concept by setting the Rhinemaiden scenes in the lee of a large hydro-electric dam, as part of a 19th-century Industrial Revolution setting for the operas. For the scene with Siegfried in Götterdämmerung, Chéreau altered the perpetual youth aspect of the Rhine Maidens by depicting them as "no longer young girls merrily disporting themselves; they have become tired, grey, careworn, and ungainly". Since this production "the assumption of unrestricted interpretive license has become the norm". For example, Nikolaus Lehnhoff, in his 1987 Bayerische Staatsoper production, placed the Rhinemaidens in a salon and had their lament at the end of Rheingold played on a gramophone by Loge.

Cosima