The rumor is that "Pro" models will use the new chipset while the current models will continue to use the still rather excellent A15.

However, I believe the rationale for that is that A16 chips look to be in extremely short supply due to lack of capacity in the next generation process foundaries.

So rather than place a hard limit on the number of phones Apple can ship, the limits will instead be on the number of "Pro" phones they can provide.

This step between the Pro and non-Pro models has been a long time coming, and may even be beneficial in keeping the price of the non-Pro version of the phone from increasing.