Zoning specific areas based on income level is really a weird way to approach the problem. Something I heard about happening in the EU is that for something like an apartment building, they are built to house people from all income levels or rather maybe it is built with different sized apartments/flats. There should be no reason that a 3000sqft 4 bedroom apartment on the same floor as a 1500 sqft 2 bedroom apartment and/or a 800 sqft studio. It might actually make it easier for architects to solve problems if there were varying space sizes vs. an entire building of "luxury apartments" all the same.
1. The market can not produce below-market-rate-housing.
2. The size of the construction loan correlates to the market segment of a development project. Building 80 high end dwellings requires a larger loan than building 80 low end dwellings. Banks like to make big loans. 10% of a lot of money is more money than 10% of a little money.
3. The amount of effort does not correlate to the market segment of a development project. Entitlement of 80 high end dwellings is much easier than entitlement of 80 low end dwellings because jurisdictions get more benefits from rich residents than from poor residents.
4. Scarcity of good affordable housing is the historical mean.
5. Real-estate is where wealth is parked, not where wealth is generated. If you have a billion dollars, your problem is keeping it not growing it.
6. Housing is the lowest and worst use of real-estate in the hierarchy of development because its economic value is not tied to the economic productivity of its use.
Good luck.