I want to write about a Type III civilization.  This will be set about 5-10 million years in our future.  The human race will no longer exist; between bioelectronic advances and natural selection, we will have evolved and modified ourselves into a very different species, the details of which I have yet to work out.  Type III means we have completely terraformed and colonized every habitable system in the galaxy.  We have been at this threshold for several millennia, and are starting to strain the galactic system with our demand for its resources.
 The basic plot will center on the efforts of a few brilliant scientists to develop a new mode of extragalactic travel in time to relieve the pressure before the otherwise inevitable result of galactic famine, war, anarchy, and general decay.  This is necessary, since normal hyperspatial flight is far too slow to solve the problem.  People don’t want to go aboard generational junks, and several unpleasant results from recent sleeper ship experiments remain clear in the public’s mind.
 The secret lies in using a recently developed mathematical model to unlock the blueprint of reality.  Theoretically, if one could travel through the fifth dimension, one could take shortcuts through hyperspace the same way one can travel through hyperspace to take a shortcut through normal space.  The realization of this theory would allow essentially instantaneous travel anywhere in the universe.  (We already have mastered this for sending information in the form of EM waves, which enables constant communication within the Milky Way; the problem lies in extending it to normal matter.)  Someone will eventually figure out the key, thus saving the galaxy.

Notes:
ET:  We never encountered any traces of other sentient life anywhere in the Milky Way during our long expansion.  Apparently, we were the first – and only – civilization to evolve in this galaxy.  That doesn’t mean we’re the only ones in the universe, though, as the first extragalactic settlers may find out.
GOV:  The galaxy is governed by a rational virtual democracy.  Advances in technology allow everyone to directly take part in government.  There has been peace for 500,000 years as a result.  However, given the current unsettled state of the public consciousness, some malcontents have given thought to being master of more than themselves.  A few are even determined to ensure the scientists’ failure, by any means, so that they can rule their own little part of the galaxy when chaos ensues.
REL:  There is no religion.  Everybody is a rationalist.  The quality and quantity of life have been elevated so that people have a longer time to learn about and understand the universe, and so they can die fulfilled.  Immortality is probably technically feasible, but almost nobody has pursued it, since it would lead to an even bigger population problem.
SOC:  There will probably be lots of social customs put in, but I have no idea what any of them will be yet.
ECO:  Good old capitalism reigns supreme, except with a logical basis, so that people are willing to accept lots of short-term pitfalls for a long-term gain, which offsets the profit motive, leads to stable growth, and discourages conspicuous consumption, which is undemocratic anyway.

Intent:
 This story will probably sound a lot like Isaac Asimov’s Foundation series, except there are no robots or psychohistory.  I was always intrigued by the last book in the series, when Asimov suggests we have to colonize our galaxy to be prepared for a threat from another.  Unfortunately, he died before he could ever spell it out.
 As interesting as it will be for us to begin colonizing new worlds in the near future, the idea of colonizing new galaxies in the distant future holds even greater excitement for me.  There are an estimated 100 billion stars in our galaxy, and an estimated 100 billion galaxies in the universe.  With that many people working together, there is no problem we cannot solve.  We may finally be able to comprehend the entire origin and structure of our universe, and learn whether there is anything beyond it.