Choose Between Log-in Themes? (Concept)

And idea I've had for a while was to be able to choose between the current log-in themes. For instance, we've been quickly switching between themes for the last month; the themes being Ivern, Star Guardians, Worlds, and the Teemoing. It'd be cool to be able to choose what log-in theme we saw, but it should be limited to what log-in screens were currently active.