Back when I was in the army I DLd some FL mod that did just this, albiet in a beta stage with NY/Texas and a few other systems merged.
You could even fly from one system to the next and Zoners, pirates, BHG, IMG and what not even had the occasional base in the middle of deep space........ but that said it would take hours to fly from one system to the next.
I vaugley remember that the guy that did it did something to get sued by micro$oft but dunno if it was connected.
And no I dont have that mod anymore, lost it many years ago.
This, not a good idea, but I do kinda like an idea of all Sirius being connected, with the exception of Nomad and Guard systems. Like before the days of jump gates, trading was done manually, took a long time, but it was the only way! However, I do think that it should be the same as it is now, jump gates and jump holes still exist, but instead of popping at the edge of the system, you enter the system bordering in that direction. It would make it more strategical to attack Liberty/Rheinland or Kusari/Bretonia for the war, people come from no where, flanking the battleships, however it would have to take awhile to get through a system, like it takes about 5-10 seconds to get through New York to California with a jump gate, it would take like... 30 minutes just on cruise. System chat stays the same however. But this probably isn't possible, so oh well :/
EDIT: Just read the two posts above me, kinda makes my post here stupid, but still, +1. So good enough!:P