If you have already found a therapist who is interested in a deal like this, and you can back yourself, I think it is a very good plan. It is especially nice if you don't have to "buy out" the practice. And, phsing you in, makes a huge difference in how the transition goes.
It is rare that one finds a therapist willing to go this route, but I wish more therapists would use it. It not only helps the outgoing therapist and clients, but the new therapist as well. A win-win-win when it all goes smoothly!