This is just a hypothetical situation, although its not bad to dream about it.
I'm wondering how would this lineup work if these guys played at the same time. Man, that gotta be the biggest and most suffocating lineup in the league. All of them are versatile defenders. While Durant is not an All-NBA defender, he is not too shabby on that category either. Then add legit rim protector (probably Zizic or some FA).
In cue of pessimist of Durant's possibility, this is just a hypothesis. Whether you want to get excited about signing Durant or not is up to you.