I, the god of my world, have managed to create what I think is a new kind of monarchy! (sticks out chest in pride) Despite my continued insistence that this monarchy is completely different from others before it, the people keep thinking about the classic forms of monarchy...more on that later.
The monarchy (I prefer to call it a democratic monarchy) exists in our far future: it spans multiple star systems, but does not rule over the entirety of the Milky Way galaxy. I decided that I hated the classic forms of nobility and instead chose to expand the royal family, those who would definitely have royal blood. I mean, the empire is larger than those previously seen in history...
The Emperor/Empress, instead of directly ruling over the Empire, instead heads the Judicial branch of government (judicial, executive, and legislative, hence the democratic monarchy). While the Emperor/Empress can directly rule, usually it falls to the Crown Prince/Princess to be the head of the executive branch. The legislative branch is headed by the Imperial Assembly, which is made up of representatives from the various planets in the Empire as well as sovereign states (either sovereign states that exist on parts of a planet much like today's Earth nations or sovereign states that consist of several planets).
Setting aside the Imperial Assembly, the Crown Prince/Princess usually succeeds the Emperor/Empress when he or she dies. When this happens, a new Crown Prince/Princess is chosen from among the children of the royal family. (I think there is an age range to qualify someone for this, but dear me, I haven't paid attention so closely yet.) Part of the democratic process comes from this election/coronation: All of the eligible candidates (setting aside those who voluntarily decided to give up ascending the throne) would be in the running, trying to prove their case through their past accomplishments, and sucking up to the people. (How these humans manage to ascend to the throne is currently beyond me, I have other things to focus on.)
Now, the Empire also happens to be in a world where magic and psionic powers exist. It was founded after a cataclysmic world war that drove almost all of the people who could use magic and psionic powers into space, who knows where they all went? The catch here is that people could suddenly be born with magic and psionic powers, so over the years the population with those powers would slowly form and increase in number. To counteract any sort of traditional assassination attempt, and some other reason, the first Emperor decided to have multiple children, and encourage those children to have multiple children, so even if not all ascend to the throne, the royal bloodline would theoretically be hard to kill off. (Mates for members of the royal family would be taken from the people of the Empire, though. God says no incest and inbreeding a la Hapsburg.)
The other reason is that since this Empire is based upon a rather unorthodox monarchy where one family bears the burdens of leadership, it would be cruel to force leadership upon those uninterested in it, or those whose talents are needed elsewhere. So having multiple children would increase the chance of capable royals serving in government in appropriate places, or even serving the Empire in the public sector.
But there are no (scoffs) nobles. All members of the royal family are considered as royalty a la Britannian Empire (Code Geass).
How would society in the Empire, as well as the inner politics of the vast royal family, work out?
Extra) Would there also be internal power struggles in the royal family and how would it work out? (The kind where after the Crown Prince/Princess was chosen, another candidate decides he or she is better fit for that role, or even as Emperor/Empress.)
Extra) So there are those people who absolutely slobber over the idea of a more classic authoritarian monarchy, instead of one corrupted by democratic ideals. What sort of civil wars would erupt in this empire over these two differing forms of monarchy?