Joseph – some of your historical info is still incorrect. In the know, astute readers will notice that.
Yes, there has been some movement to Hasidism. However, the picture you are painting misses large numbers of Oberlander who have joined other segments of Klal Yisroel, such as Yeshivish, Litvish, regular Ashkenaz Shuls, as they voted with their feet and left when some Oberlander institutions came under Hasidic domination (e.g. R. Katz of Vien was/is Hasidic, not Oberlander who converted, and he violated agreement when he was hired to keep things as they were). In Williamsburg Vien there were like no old Vieners left, so R. Katz brought in Hasidim. It was not that old Vieners converted to Hasidism there.
Furthermore, even those Oberlander who allegedly became Hasidic often retained some Oberlander Ashkenaz identity and minhagim, so they did not totally leave where they came from. E.g. I think Dushinsky says bameh madlikin Friday night, people put on tefillin on Chol Hamoed, etc.