Admins could modify the activity, but users can verify from outside (if they so which). If the user data gets obfuscated, it becomes a complete black box.
But then you have two different events.
Here is one problem: the userbase on the Fediverse is already ridiculously small. If we keep dividing ourselves over every little preference, we will end up with nothing but a thousand little ghetto fiefdoms, used by people who will never ever learn how to tolerate a different point of view.
No. What will happen is that the silent majority will want to keep federation with everyone, but the intolerant minority will keep pushing instance admins to defederate from anyone who does not want to obfuscate votes. Eventually, LW will make a decision one way or another and everyone else will just have to decide if they want to stick with their principles or follow the leader so that they are not isolated.