'Advanced Start' slider. Let the AI run things for [0 ... 200] years before having the player pick an empire to take over.
HRE scenario. Do the above, then take the largest empire and make each planet in it a separate empire as if they were taken over by separatists, and you play as one of them. All of them have a mutual defense pact with each other against outside aggression only.
Random or Selected Empire Backstory. Default is 'pre-FTL species just discovered space travel'. Other options could be 'part of a fallen empire that broke away and lost most of their tech', 'space nomads looking for a home' (start with a colony ship and a negative income), 'refugees from empire X that colonized a new world', 'enlightened protectorate of empire Y', 'liberated fragment of empire Z'. X, Y, and Z would have to be advanced-start empires with several planets.