[tenebrisalietum]

Letting imagination run wild here...

Naw, they'll be replaced with national citizen IDs or simply nothing and you must apply for a federal ID to see or get benefits.

Regarding such an ID, I bet it would not be technically required unless you want to receive some sort of federal benefit or participate in a federal election. They might not even call it a federal ID, something like "National Citizen Verification" (NCV)

I'm sure that incentives would strongly align for you to have one (or start more expensively starting to get one) if you participate in federal court, get arrested by a federal officer, or go to a federal prison. Also joining the military would likely result in you and your spouse getting a free one. If the draft is reintroduced at some point in the future, then it'll become common quickly.

Of course they'll still have the SSN format because of existing legacy misuse of the SSN as a national identifier. But maybe not. Every bank I've done business with wants my state driver's license number, of which a birth certificate is a requirement. Maybe it's someone's idea to simply give banks access to those databases.