I'd be leery. What if the home doesn't appreciate but loses value? You'd still be on the hook for paying back that initial 10%, plus the mortgage, even if it's underwater. And I wonder if a bank would be eager to approve a large mortgage, if the down payment comes with a lien like that?

It's a shame that "the utter dearth of affordable housing" leads to financial schemes like this....instead of more affordable housing.