My idea for a new episode is to have peter cheat on Lois a few times with a few women. I say it because Lois has cheated repeatedly through the series and peter always took her back with little problem. The only time peter really cheated and really did not exactly mean it like lois is when he slept with a few guys not by choice through the series. It made it unfair with the way Lois cheated.
And one episode about stewie going to the future to make sure he has taken over the world but finds out the only way to do so is time jumping to a few turning points in his own life and change them to deseried outcome.