Well, I can tell you, that the average Australian finds it disturbing to hear an American speaker.
Nothing against our friends in the USA, but in Australia, there is a more reserved culture (as there is for many other English speaking places such as UK, New Zealand etc)
To have a "tall poppy" from the USA give a talk, (instead of a local brother) will only alienate the locals more and more....
The GB have to see that the novelty of having their big old faces up on a screen has worn off amongst witnesses.