Rebate/incentive programs made sense earlier in other cities to encourage pilot efforts and help the industry ripen, just as occurred with solar and conservation in the  late 20th century.  That stage is over: materials/installers/technologies/best-practices are fully tested and established, and codes have change to fully incorporate green roofs (just as with solar).

And the cost-effectiveness is also fully demonstrated. This is good for tenants, owners, developers; whether market rate or affordable or condo (or a public project).  It reduces, not adds to the cost of housing (a six year payback on a 50-to-100 year building benefits all: affordable housing and public projects most of all). Furthermore, it adds to the value and marketability of projects, which benefits speculative development or shorter periods of initial ownership.

And the benefits are to all. Good math is good math!