Strangers and stray dogs on the premises will trash the property. You can't run two schools within one building at the same time. You can't run two schools, a soup kitchen, a night shelter, and a teacher training programme within one building, at the same time. Teachers always grumble. Children need to be protected from the harsh realities of life.
Good fences make good neighbours.
Competition is the best way to motivate pupils. You must know where the money is coming from before you make the plan. Principals get stale if they stay in the same job in the same school for too long. You can't change the basic structure of how a school operates. Freedom is dangerous.