KIPP schools demand a lot of their teachers, who work very long hours and are required to be on call at all times. They pay a bit more for this, but only a bit, and this isn't a model that scales well. You can always find a small cadre of dedicated young teachers willing to put up with this, but you're never going to find the hundreds of thousands you'd need to make this work on a large scale.
How big can this go at the end of the day? I have no idea. But there’s no reason to respond to this track record with pre-emptive pessimism. Instead the proper response is to encourage elected officials in a low-performing, high-poverty school district near you to welcome high-quality charter schools. What’s more, charitably inclined rich people should strongly consider closing their checkbooks to well-endowed universities and opening them to non-profit institutions that do an excellent job of educating poor kids. Institutions like KIPP.