The proposed $4.3 billion merger of single-family rental operators Invitation Homes and Starwood Waypoint Homes will create a corporate landlord with 82,000 homes – and a behemoth of a potential client for Fannie Mae and possibly Freddie Mac. Earlier this year, Fannie agreed to provide Invitation Homes with $1 billion in financing. The deal broke new ground for the government-sponsored enterprise, but it also raised questions about whether a government-owned entity that received billions in taxpayer assistance should be lending money to a company (Invitation Homes) grubstaked by Wall Street. Since the Invitation-Fannie arrangement was unveiled, no other significant SFR financing vehicles involving a GSE has...