There's no Federal agency that can decree that sort of policy. Coal generator retirement happens on a state-by-state or even business-by-business basis.

Some states are going to cling to coal power past its economically rational lifespan because important parts of state politics are linked to coal businesses. States where coal retires for economic reasons will go for least-cost replacement (a blend of solar, wind, and natural gas). States where environmental concerns trump cost concerns have little if any coal generating capacity left to replace at this point.