Why should proposition 2 be remotely true? What we are doing with DF, and The Sims, and Sim City, etc etc, is playing god with a simulation of humanity. This shows conclusively that human kind likes playing god, or some significant fraction of those able to do. Posthumanity comes from humankind, therefore will have some similarities. There is no reason to assume that playing god will be less attractive a past time for a posthuman.
God-playing starts early for human beings. We start as children playing with action figures and dolls, no matter our culture or technological advancement level. As we get older and more mature, our god-play does not lessen, but rather takes on more advanced and explainable terms. Instead of dolls, we play video games, or pen and paper rpgs. In hours of our lives which are not play, we still imagine what it would be like for our children, plan things out, and similarly play god there.
So it can be seen that as human beings mature, both physically and culturally, the desire to play god does not lessen, but strengthens. Posthumanity being a natural extension of the maturing of the human species, we cannot assume that this curve, so established, will deviate from that course.
I cry shenanigans on all three of those postulates, since none of them is provable, and at least one of them seems directly counter to an honest assessment of the human condition and our current direction of advancement.