Qualified Opportunity Funds (QOFs, which invest in Opportunity Zones) are not eligible as replacement real estate in a 1031 exchange. 
For those with questions about investing in QOFs as an alternative to a 1031 exchange, you can review the proposed IRS regulations at https://www.irs.gov/newsroom/treasury-irs-issue-proposed-regulations-on-new-opportunity-zone-tax-incentive.
