So, here we are at mid season / show finale. At the end of season 3 / begining of season 4 I thought creators had 2 options:
a) never find Earth, leave it as a myth and somehow form a new peace with Cylons (happy end) or destroy remaining of the colonies (sad end)
b) discover Earth. Interesting enough, I always thought they'll discover *us* in early stage of developement or in our real-time, with our technology at the stage much lower then we've seen in the show. Never crossed my mind that they could arrive in *our* future time.
Arival at post-nuclear disaster is a very clever plot developement cause it sends our protagonist and antagonists a very clear message: WAR is bad thing. Also, with no living thing on Earth, authors do not have to acctually deal with complications that would normally arise, such as our technological and society stage of developement, global *politics*, leaders, followers, in short - our own issues... This is also great as show now brought another theme in main focus: destructive nature of a mankind (this all happend again, and again, and again - said by a hybrid).
Then where this can get us in the remaining of the season 4? Well, I think it is the obviuos now: Humans and Cylons will have to co-exist together, since now they are all mortal and will accept the task of restoring life on Earth. In a more interesting way, human race may eventually die, while Cylons with the final 5 will continue to live and bare the memories of human race which will in literal way *evolve* into new race (like Cylons actually did) (Starbuck: in order to child reach it's potential, it's parents must die).