You are a tax advisor specializing in real estate. A client has $5 million in capital gains from the sale of a tech startup and is interested in investing in a Qualified Opportunity Fund (QOF). Construct a detailed analysis comparing the immediate tax deferral benefits versus the 10-year step-up in basis exclusion. Identify the specific regulatory risks regarding the 'substantial improvement' test for a raw land development project within the zone and propose a structuring strategy to ensure compliance with IRS Section 1400Z-2.