Azura states that the Scar means that "For the first time in centuries, we can look up and see real clouds, real stars".
In the books although the people of Trantor don't enjoy the outside they are forced to visit it every year as children. This itself is a nod to Asimov's earlier Robot novels, most notably to Caves Of Steel. In the Robot novels mankind's retreat into the protection of an enclosed world causes stagnation and threatens it's existence. It is only by leaving the cities that the humans of Earth ever break free to found the Empire in which the Foundation stories are set.
The subplot of the Invictus is made up for the show, but it does recall the subplot of the old Imperial warship which has been found by Anacreon, who then asks the Foundation to repair it, while intending to declare war on the Foundation whether it declines the offer or not. This is in the first book, part "The Mayors".