My suggestion is to tie the background introduction to the specific game you're going to run. Try to make it as in-character as possible rather than a general overview: remember that most people in the OTU won't have a very good grasp of the "big picture" side of things. Use this to your advantage.
For example, if the characters all hail from some collapsed world (now backwater) which is just being integrated into the fringe of the Fourth Imperium, you could roleplay the players' village's wise woman or their tribal chief (probably in a "flashback" scene taking place in their childhood or adolescence) as she tells them the campfire-side tale of the old Imperium. Ofcourse, she'll focus on the more juicier parts of the story (e.g. huge battle-fleets clashing, Strephon's assassination, planetary bombardment) and ignore the less spectacular ones (e.g. exact dates, titles of people, economics and so on). She'll focus on things closer to Gushemege and hardly mention the remoter areas (e.g. Strephon, Dulinor and Lucan are going to get the front stage; Margaret, Craig, the Solomani or the Hivers are going to be only the supporting cast, if mentioned at all). She'll know some of the day-to-day facts of the Imperium (e.g. it takes a week to go from one star to another) but know very little of technical matters (e.g. what is a Lanthanum grid or how exactly does the X-Boat network operate). She might also twist the story a bit both due to the desire to make it more dramatic and due to the fact that she knows most of it second or third hand (so Dulinor and Lucan might become "brothers" in her story, conspiring against "their father" Strephon).
On the other hand, if they'll be playing remnants, you'll only have to tell them of the old Imperium, and then only the most generic things (remember that most people in the OTU aren't History Ph.D.s), focusing more on the small-guy perspective and less on intricate politics. Then play out the events leading to their entry to cryo (was their ship attacked by pirates? Infected by a Virus? Were they taken prisoner by a faction or another and then put into a low-berth? Did they join a Timer Club?). Then start the game as they are awakened by a salvage team in 1148... And have to learn by themselves of all of the 1248 stuff.