I think many people will be against it and they have good reasons, but I'm not. With One Tamriel many people from different alliances will join together and make bonds. It's a shame they will never be able to fight at Cyrodiil under the same flag...
Actually I was just recently discussing with my friends how this will be actually possible come One Tamriel, since the main issue with it before was how to handle quest progress in an alliance zone, but with all characters having access to everything at any level, and no more segregation between alliances. All ZOS needs to do is code in a way to do it and offer a method to do it (most likely it'll be in the crown store).
I do believe at some point they will add alliance change. I imagine they will do it so those not satisfied with their faction can change one of their characters to another one. But it will possibly be with a high crown price tag like 4500 crowns.
Edited by Thevampirenight on September 9, 2016 12:55AM
Alliance change can't come fast enough for me. I think they just cleared the last technical issue with Tamriel One concerning quests and scaling. I really hope it happens with update 13 at the latest.
I seem to remember, but cant find it, a video from eso live perhaps, where rich is talking about race change etc, and the only thing they wont alowe is changing class.