If we removed the current zoning density, then more people could afford to buy a plot and build a house for themselves, increasing the overall housing supply and reducing entry level prices. There may need to be some limitation on size to avoid 000s of 5 bedroom houses springing up, but this would be fairly simple to legislate.
There would have to be some restriction on this policy to safeguard say national parks, but broadly, if farmers/landowners were allowed to sell off marginal land at a maximum price of agricultural value plus 50 – 100%, this could help bring housing supply back into balance.