I have heard on various occasions that modern day keigo was borrowed from Kansai-ben. It states this on Wikipedia:
Historically, extensive use of keigo (honorific speech) was a feature of Kansai-ben, especially Kyoto-ben, while Kantō-ben, from which standard Japanese developed, formerly lacked it. Keigo in standard Japanese was originally borrowed from Kansai-ben. However, keigo is no longer considered a feature of the dialect since Standard Japanese now also has it. Even today, keigo is used more often in Kansai-ben than in the other dialects except for the standard Japanese, to which people switch in formal situations.
but I can't seem to find any credible sources. Does anyone know of any credible sources or more info on this?