They reference the second season so much that it almost makes the 3rd, 4th, 5th, and 6th seasons irrelevant.
Miguel never comes up.
Trinity comes up sparingly. The last time was a Dex filler episode where he and the ghost of his brother drive up to the Midwest for whatever reason. The kid is still alive, so it COULD prove to be a loose end, but I doubt it.
Lumen is in the wind, another loose end, but I don't see her coming back.
The only thing that came of the sixth season was Deb finding out at the VERY end. Other than that, the sixth season never comes up.
I just find it odd that the second season was SO important. It comes up all the time. It makes seasons 3 and 5 (his partner seasons) especially worthless.
The only way that I see them tying all of these other seasons together would be some sort of insane royal rumble at the end of the season where all of the loose ends come back to kill each other. Unless Dex gets ratted out and these people get tied together in the end. I highly doubt either of those scenarios.
I still maintain that the old woman story arc is going to be done halfway through the season. Just like the mobster last season.