1) Sure, some operations are commutative and compatible, and you can import them from one branch to another, but in the general case, they aren't 2) Same thing

1) Sure, some operations are commutative and compatible, and you can import them from one branch to another, but in the general case, they aren't 2) Same thing that happens currently on Wikipedia. There's a set of rules that determine what edits are valid and which aren't, and a local client can applies those rules (or not) to determine the HEAD version. There's nothing that prevents a Sybil attack on Wikipedia, but there doesn't seem to be the need for it.