I chatted with 3 separate Samsung reps about this and, as predicted, got three different responses. One stated that the unlocked update is already out, but is being rolled out in waves and my wife's S8 just hasn't gotten it yet. Another stated that Samsung is still working on it and they have no timeframe for the rollout. The third rep stated that Samsung is rolling the update out to the carrier variants first and that the unlocked variant rollout will begin next week.
The explanation provided by the third rep seems more plausible than the other two, as the rep provided a lot of details. Take that as you will.