So that's what happened to me last Monday

Was on what looked like an all-US-metal itinerary, SAT-PHX-PDX, and upgrade for PHX-PDX cleared normally but SAT-PHX was a CR9 and had the "upgrades not offered" text.

During OLCI I was offered the ability to choose a seat in F for $0, did so, and when I got to the airport discovered the CR9 was in new-AA livery with an AA interior. Wonder if this is re-jiggering of the schedules + fallout from the Envoy downsize?