A recent thread touched on CLTs. In NZ the government has an obscure loan facility for Maori housing on collectively owned land. Lateral social collateral is also starting to be talked about here, especially by ethical investment outfits, whereby peers guarantee loans, but usually only to small amounts.
Land trusts are a great way to keep land off the market rate real estate appreciation cycle.
The downside is that financing may be much harder or impossible under such limitations. Banks really don't like to finance homes they can't easily sell if they foreclose, and since you would not have clear title to the land under a land trust, only a lease, it would be that much more less appealing to a bank. However, some banks do have special loan programs targetted for low income families, some states even require large banks to invest some small percentage in these programs. Check with your local bankers before committed to such a path.