They actually let it slip that the reason it's taking so long is because it's being split up into three separate DLCs like the similar upcoming pack for TSW3 will be.
I was under the impression from what dtg_jd said previously, that they were just waiting for the split ("separate" BKL/SKA/SPG) store pages to be "live" to release the "New Journeys" DLC. Which are live now, but the DLC still hasn't been released.........
I guess with locos detaching from routes it enables them to re market that pack individually by loco, perhaps with some other jazz offered to open up peoples wallets