True there are no victory conditions at all. Ultimately, one power will become the strongest amongst all. If a victory condition is really needed, it would be survive and defeat all other players.
And also its correct that it will turn out to be an open-ended game will maybe double or triple game time of the original game.
The reason this house rule is developed is that me and my friends often find ourself in the position of becoming dominating powers as Russia, Germany or the USA but still want to continue the game and expand our hard-built empire. At the end of the day, it is just a house rule that me and my friends loved and would like to share with other A&A lovers here.