Undisclosed nothing. It has been a known fact that the Imperial Navy had J6 couriers since CT:Fighting Ships.
Oh, right, the fleet couriers. My bad, forgot.
It's also implied by the ship construction rules that civilians can build J6 ships, which in turn implies the existence of J6 commercial passenger liners between high-population worlds.
TL15 civilians, which limits it somewhat. Cost/benefit considerations may also set certain limits. A J6'er costs quite a bit and loses a big chunk of space for jump fuel. We have some hot fast combat jets nowadays, but the commercial stuff seems mostly quite happy with subsonic speeds.
Aramis did a cost/benefit analysis some time back. If I recall, you really gotta put aside the cargo and passenger cost rules so you can charge the rates that make express transport feasible. You can sideline cargo transport and do the buying and selling bit to make the money but, with the jump fuel rules, the mid-speed ships ends up carrying about as much cargo or more per month as the express runners, and they cost less. It's still more profitable to build a slower ship and take more time to get to market. Jump-6 is a specialty niche - but you're right, it probably exists between the higher pop worlds. A large enough population pair generates enough traffic to keep specialty flyers happy - assuming you let the rates float instead of mandating them.
... The politcal faction that Santanocheev belonged to started looking like idiots several years before he bacame their poster boy. Norris's petition to the Emperor reached him (the Emperor) in 1104 ...
I have no information on that. What did they do that was big enough to warrant the Emperor's attention on a remote sector three or four years before the shooting started, and why did it take him that long to make up his mind?