YO – yes you are dreaming. I agree with you that everyone should speak Hebrew, but unfortunately it’s not the reality. So practically, speaking yiddish is probably more unifying than Hebrew at this type of event.
Personally I was at the last siyum hashtags and was very turned off by the Yiddish speeches. Maybe it was one or two I don’t remember how many I just remember being annoyed. A real waste of my time. But I guess it’s nice for those who don’t understand English. It should be kept to a bare minimum.