Why can't we hint the first replica?
Well, actually I think we could. Or at least if we cannot I forgot why. We would need to be sure we never replay an hint twice though, which I'm not sure is a guarantee right now. Also, we can only make this if what we store as a hint is the serialized mutation (in this case, the serialized CounterMutation): we can't apply the CounterMutation on a non-replica (partly because that would potentially increase the counter context too much, partly because counter remove suck, which would probably be a problem at some point).
So it should be doable, but it's a bit of work.