This is a bad idea. It is unfair to people who, even with the subsidy, cannot afford to buy a home and those who prefer to rent. Because it is a demand subsidy without any corresponding price controls, some of the money will also just get captured as higher home prices, negating the affordability goals of the policy.

A better idea that is thematically related would be to take the annual cost of this program, divide it by the number of people who turn eighteen each year, and then give the resulting dollar amount as a lump sum to people when they become adults. If they want to use it for a down payment, then they can. But they can also use it for college, buying assets other than owner-occupied real estate, or whatever else. This policy is sometimes called a demogrant and was, for a time, all the rage in the racial equality world, typically sold under the name of “baby bonds.”