Just a note to followup on my experience in case it's informative to other people. My automated seat swap was from 21K to 31L. 31L being an E+ bulkhead window. I would have been less upset initially had I realized that, but the seat map didn't make it clear that the seat was E+ much less a bulkhead.
At the airport, I inquired about how they were assigning premium plus seats and didn't really get an answer. At check in, the agent said she didn't know. At the gate, the agent first said it was treated as E+ and "those people paid for those seats." I gave her my boarding pass and she sort of huffed and said she would add me to a list but that there were several people ahead of me (she pointed to a hand-written list she was keeping). I expected her to say the seats were being kept for 1K/GS, but she didn't.
Of course, I didn't make it off her list tough. That said, I sort of regret spending the time thinking about it/calling. The new seats didn't seem that much better than the E+ bulkhead from my quick in-person glance at them.