I think the closest we could get to having everyone being the god-emperor would be to somehow restart the primarch program, which is near impossible considering all the equipment is lost apart from some primarch gene-seed that (I think) the emperor's children have.
If the imperium can retrieve that then it's theoretically possible (I stress the word theoretically. The chances are a trillion to one).
But if they can do it, humanity can curb stomp every other race and rule the galaxy (imagine billions of Angrons, Magnus', Dorns and Perturabos running about everywhere). Then a golden age would last until the inevitable happens and a civil war starts and we would be back to square one, except it's just humans fighting each other.