I wonder the same thing... although right now, if you combine, say, a YQ-free airline on the longhaul and a YQ-charging airline on a short connection, you don't get YQ on that leg. So hopefully that logic will apply here.
Plus both UA and SK are YQ-free anyways, aren't they? So you'd have YQ waived for AC segments, and then you'd have to add the YQ charged for UA and SK to that. So perhaps $0 + $0 = $410 in AC math.
We'll find out real soon. You're right. This is going to be "fun."