Okay, Thoughts:
On in-system FTL
What if the fuel requirements per length unit increased exponentially? Due to, say, overheating of the jump drive? This would make it necessary to stop frequently to let the engine cool off, thus allowing only short FTL hops, and rendering interstellar travel via the FTL drive uneconomical.
Perhaps we could change the way fuel works somewhat: use one-jump ships, change the "refuel ship" button to "cycle coolant" or somesuch, so that you can use planetary resources to cool off your jump drive faster. In liu of this, we could use ramscoops to slowly "cool off" your engine while in space.
On interstellar issues
I suggest that we do have interstellar colonies. They were established some time ago by flotillas of generation ships carried by solar sails. However, since the closest is 4.3 years away at light speed, it's not really possible to do much more than trade research papers twice a decade.
This sets up an interesting scenario if we want to bring in a large-scale adversary. Imagine if one of the second-generation colony systems (colony of a colony) who had been lost, or had no contact at all with earth was able to develop an efficient interstellar FTL drive and invade their neighbors? We'd never actually be able to visit the neighboring systems (unless we were really bored and wanted to visbit out ten or twenty other complete systems until interstellar FTL is discovered), but we could hear about it in the news or find ourselves threatened by said invaders.
On politics
This necessarily has to be more realistic than most other EV plugins, because it's more immediate. How do we deal with the fact that as it stands, modern space angencies are nowhere near ready to do anything but fight with eachother over resource shortages in the middle east? We need a motive for exploration, and that has to be resource acquisition. Obviously, nobody is going to find oil in the asteroid belt, and I can't really think of any metal that's so precious we'd send an expedition all the way to outer space to collect it.
So let's suggest something new. Some new, post-nuclear superweapon which requires an ingredient so rare on earth that it's worth sending out extraterrestrial expeditions. A mining colony is established, the products are shipped back to earth, who then proceed to use them to destroy most of civilization and set themselves back at least five centuries. With the nice, green, self sufficient earth out of the picture and a bunch of resource-starved stranded in the asteroid belt, colonization finally becomes logical. Set the story some centuries after this event - Mars is a self sufficient colony in certain domed and protected areas and is well on its way toward being fully terraformed. We have colonies in the asteroid belt, the trojan asteroids (clusters 60° ahead and behind the orbit of jupiter), the jovian moons, research posts in orbit of/underneath the atmospheres of titan and venus, and a whole crapload of stations in orbit of every single body in the solar system. Earth is well on its way back to space-age technology, but there's been such a huge cultural gap that misunderstanding is bound to take place.
Speaking of which, this opens the opportunity for a crapload of multicultural niftyness, a la The Frozen Heart. What if the initial mining colonists were asian/pacific in origin, and you have to employ some not-universally-effective translator at every non-terran port? You could have indecipherable pictograms in faded blue print overload by the not fully coherent output of your translator.
And other nifty stuff.
-reg
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"Oh crap. I'm going to hell - I put the Bible next to Mein Kampf again."
-Her Holiness, Pope Jenne "Kirby" Hubbs
