Brosuke:
I would give this a look, although compared to a god game, this seems more like a cooperative writing game than a full-on RPG, since there isn't really a player avatar to speak of if I understand the concept correctly. Would it be possible to have some kind of immortal leader role, like in the Civilization series, or is that too far from what you have in mind?
Global idea is to role-play a nation (as a whole and, if player desires to do it, each and every individual: commanders, politicians, nobles, traders, commoners, soldiers, criminals, bums...)
As for leaders, initial idea is to have multitude of them; different, vulnerable, mortal. And the game taking place in parallel universe, but on Earth. Different landscape, but same physics/resources/animals. Different civilizations, but same eras advancement paths (so no steel before bronze, and no helicopter tech rush).
BUT, I personally love godgames, so in short the answer to your question is no, it's not a stretch at all for me, to let you all play immortal rulers. As I said, I'm totally up to any adaptation as long as rpg element stays ...
IF that adaption is what everyone agrees to. Because I can guess there might be people who would want to play a realistic version of leaders.
By the way, have you played/seen Crusader Kings game? The idea there is that you play a mortal leader who (usually) has a lot of influence on his heirs, their upbringing and training, and once your leader dies you just play next heir in line of succession. You can always come up with something like this. Some strong undisputed rules of successions, strict and highly secret heir upbringing and tunneled training, up to the point that your entire nation might actually believe its the same immortal person ruling them through generations. This way you also get A TON of new rp possibilities, and even some character flexibility (if you as a player ever decide you want to spice things up a bit). Hell, even if your leader and all heirs die (due to some weird gm brain lag? idk, I don't usually play against my players) You can always come up with another family/caste/political group/some random sect of fanatics/rogue guild/whatever-your-imagination-would-allow deciding to take the throne, discovering tomes/scripts uncovering the truth, describing upbringing and training secrets. That group of people might easily come to one and only correct conclusion: the only way to rule this nation is to continue with this biggest fraud in history...
Would it be possible for you to play this kind "immortality", or is it too much of a stretch for you? ;)