I have recently become aware of a Nusach difference in Kaddish. In the pasuk starting Titkabel I have noticed that people davening Nusach Ashkenaz are very particular to say d'chol yisrael and not d'chol beit yisrael as they say the latter is Sephardic/Hassidic and not genuine Nusach Ashkenaz.
I looked at various siddurim. The Roedelheim, Singer and modern Koren siddurim all have d'chol yisrael. The Artscroll and (I think) Birnbaum have d'chol beit yisrael which these people say is a mistake.
I am looking to understand where this differentiation comes from, and why it is considered a Sephardic/Hassidic minhag that mistakenly crept into Nusach Ashkenaz.