Well the most telling sign is that the other vehicle configs (AP2.5 + MCU2) have multiple confirmed HW3 retrofits but no MCU1 or AP2.0 vehicles.
Elon officially states that it is possible but without a clear timeline. I wouldn't be surprised if they are trying to do something in software to make MCU1 work well with AP3 since there's a large cost to MCU2 retrofits.... But unless Tesla tells us more, we are left to guess.
This right here. They are just buying time to avoid having to replace MCUs. The longer they hold out there fewer cars with mcu1 are on the road. Expiring leases, trade ins etc