In 4.84, it was the Diamond-Niobium route (I was running Lux food-Boron like a newb), when the mining came out, there was the pennsylvania silver rush, I think, and the Dublin gold rush. All of these brought large numbers of people to certain lanes in Sirius, because they were the most profitable routes. Now, I have two ideas which could get more people trading, and more into groups or factions.
1. Raise mining profit back up again, but wait, there's a catch. Mining ships only get 1000 credits per unit, wheras every other ship type gets the full amount. This means that the miners are going to have to use *gasp* teamwork to make a good profit, which leads to more interaction between players, and so probably more impromptu groups and faction membership. Also, to those of you who are thinking that people will just leave the mining ship for transports with mining turrets, allow me to remind you of the fact that a mining ship gets an 80% yield boost (which could in fact be raised even further to encourage mining ship use)
2. Every 24 hours, a random route's profit per unit increases drastically through FLhook (say, 1000 per cargo unit). This lasts for 24 hours, but for the first 12, the majority of traders won't know about it. For the second 12, this information can be found by typing "sten stocks" or something. However, the factions that operate in that area would be sent automatic messages (possibly based on the /fm command) every 10 minutes or so right from the start of the bonus cash, giving the details of the increase. For example, Southampton shipyard needs an enormous amount of engine components and its stocks are low. Profit increases. the FLhook thing gives all Bowex), BMM- and Gateway) ships an /fm that engine components are in demand on Southampton. 12 hours later. this profit increase goes public to anyone who types "sten stocks", so you get independent traders flying the route, and after 24 hours, the profit from this route goes back down and another one becomes very profitable.