About real emperors
There is notion that an emperor is someone who is in power only because he is making sure other powerful factions/personas in the empire are content. I agre, that's the most intuitive and maybe even the most common case. Yet, there are exceptions, it's not the only model possible.
For example look at Russain Tzars. It was such an absolute monarchy I'm not sure we can even talk about a feudal system anymore. Traz was able to do basicly anything with anyone regardless their nobility status or wealth. They even invented "ranks" as if some sort of RPG levels http://en.wikipedia.org/wiki/Table_of_Ranks
Another example could be a king of France Luis something (the one they called the Sun). He turned all nobles into courtiers, they were preoccupied with their artificial statsu on the court so much they ignored everything else leaving all the real power in the hands of the king (it was rather skilled manipulation I would say )
Emperor of the known Universe from Warhammer 40k (well, maybe not exactly "real" but still), except the Horus Heresy he was never to worry about other powerful people.
And the last one, I have read about some dictator in Africa (by Rudyard Kipling). All that mattered there was how many "ears" anyone had (ears means how many times you are to speak with the dictator a day/month, your real rank was of low importance). There was no track of any factions to worry about (just 2 separate secret intelligence agencies, who hated each other much more than the dictator and therefore were never to cooperate).
Oh yes, and don't forget Stalin, althrough not an emperor, do you really find any proof/lead that he cared about other powerful factions (OK, he was worried so he was organising regular purges of his henchmen)? He did not. Except the propaganda to the masses (which no one belived in anyway, I can tell first hand because I was born under communist regime) there was no dealing with "happines of other factions" at all.
I wanted to say, we don't need to stick to the "making other factions happy" model (unless you feel that it's the best fit for that kind of game).
This also bring me to the next point, let's discuss now what kind of emperor you would want to be in a game like that. What are your personal preferences? Which ideas posted so far you liked best? In short, if there was a game where you are to be a space emperor, what kind of game *YOU* wish it to be?