Just chatted with someone on the WDW website about AP sales.
I asked what time I can buy the AP tomorrow as a DVC member. Their response:
Welcome home!
Sales of DVC Disney Sorcerer Pass will begin online no earlier than 6 am Eastern time on April 13, 2023.
It seems that potentially only the Sorcerer Pass may be available tomorrow.
When I asked if I could upgrade tickets already purchased online, they said:
Yes, you will be able to upgrade your tickets over the phone with Member Services.
You will have to call, or upgrade in person.
So it seems that we will need to call instead of doing it online for upgrading tickets. Also, they mentioned 'tickets purchased through Disney directly'. I am not sure if that means that tickets purchased from other places will need to be upgraded in person.