Curiously they are still selling seats as the flight is J2 but the seat map is indeed absolutely full. So I wonder if they are planning a swap to 787-9 but haven't done it yet. Otherwise maybe have a look at the options and give them a call if you want to be proactive rather than ending up with a downgrade (as later on in the day will be less options for a reroute) - seats are available via Dallas for instance