The IRS says it will not be available to all tax payers in those states. It sounds as if it will be a fairly small number initially.

> AZ, CA, FL, TX, NY alone gets you to about 120m people.

Not quite; ~71.8 million constrained to just individual income tax filings based on 2022 stats[1]. Excludes estate, corps, gift, tax-exempt orgs and excise, but includes both paper and electronic filings.

  AZ    4,197,918
  CA   23,209,479
  FL   14,563,047
  TX   16,750,330
  NY   13,115,425
  ---------------
       71,836,199
  ===============
  US  204,434,236

Surely, only a subset will qualify.

[1] https://www.irs.gov/statistics/soi-tax-stats-state-data-fy-2...