I'm not sure where this information about Delta not having all of A is coming from? The plan is very much for Delta (and/or its JV partners) to occupy all of concourse A and a good chunk of concourse B. They are also building a second SkyClub in concourse B as part of Phase 3.
Since the gates that lead to CBP are in A, obviously there will be some exception for the non-SkyTeam international flights, but that's usually handled by A25.
This is the latest information I saw shared in September 2022 and haven't seen anything to indicate a change since then: