Sedna was close to Eris in Aries but both will only become conjunct in 2245 in first degrees of Libra.
They were close in Pisces also during most of 19th century.
They were formerly conjunct in Aquarius in 1270s, in early Capricorn in 125, in Sagittarius in 1000BC, in Scorpio in 2120BC, and 3230BC in early Scorpio (assuming my astrology software is accurate).
In 3230BC and 2120BC these were periods of great civilization change, of big clinatic change possibly due to meteor impacts. Around 1000BC there was also a civilization change between the transition from Bronze age to Iron age. In 125 I dont see anything special except that Christanism was expanding and the Roman empire starting to collapse. In 1270s there was a period of great fighting in cruzades and of mongols. So, we would speculate another great turning point around 2220, two hundred years from now.
However the thing that I found amuzing is correlating the time when Sedna was in Scorpio and Sagittarius (Egypt and Greeks, 3000-1500BC and 1500BC-0), Capricorn (Roman empire and dark ages, 0-1100), Aquarius (end of dark ages, discovery and rennascence, 1100-1630) and then Pisces and Aries (19th and 20th century) to a specific period around the world.