The cross of matter is exemplified astrologically in the Cardinal Cross. Aries represents that which moves from within to without, our spirit. Cancer represents that which moves within, our soul. Libra represents that which moves from without to within. This would be the "other" but i guess in scientific terms this would be called "information". Capricorn represents that which moves without, the external. Together this cross seems to form a Yin-Yang in my mind, but others may feel it differently.
One can consider the 8th house. When the sun is there the afternoon is on and we are rushing to finish the day's work. Anyone with bee or hornet problems on their porches know that when the sun is in the 8th house you do not want to mess with the bee nests. This is when the stinging insects are most agressive. When the sun enters the 7th house we relax as melatonin (if i'm not mistaken) floods our neural system and all seems right with the world for a time.
Now Libra represents a door or window where we are open to the external. For this door to exist means that there must be a contract with the universe based on justice and good will, otherwise we would simply board this door up and never come out of our shells. That is why Libra is associated with harmony and the benefic energy of Venus. That is also why i suspect that if there is an outer planet Yang ruler of Libra it would encompass this harmonious and benefic energy on a generational scale. The ego has to be subtle in Libra, otherwise it would simply overpower anything trying to come through and we would experience no growth or learn anything new.
Being a lifelong member of the Sun in Libra bunch (Sun Venus conjunction in Libra 2nd house) i have to admit that i don't see that Libra tries to rock the boat very much. Drama and passion are actually very energetically draining on me. harmony is more important to me than impassioned drama. i find my greatest excitement in ideas, such as reading about the Nabta Playa monoliths in Sudan which pushes astronomical study back thousands of years before Stonehenge!
If Libra is the fulcrum where outer meets the inner then we can expect there to be an interface between the cosmos and our inner sky. if we exist as a fractal of the whole, or perhaps as a holographic fragment of the whole, then we should be pretty good at recognizing when something is not just, where something doesn't square with us and we cry "unfair!" I once read that, astrologically, Libran energy has great resilience to mental disorders.(i also know that i have been pushing that boundary for a long time, :-)) That is probably due to the Libran temperament and the need to harmonize ourselves with the external.
anyway, that's just my own take on Libra, and maybe in it there are some clues on what we might find in planetary ruler(s) of Libra.