Might be my bad reading comprehension, but in the thread you linked i didnt read "we're moving everything to the US", but rather that EU and US would get separated single-server-tech implementations, as a full-scale merge of all servers existing back then was too difficult.
As for your question about a source, pls feel free to sift through the course of
this Thread.
To me the initial discuission didn't sound as if the final call mentioned on
Page 13 was already made from the start. In Nusquam's post is the first time I've encountered the inevitable nature of the move.