As someone who did not really get started with D&D until Murder in Baldur's Gate and the September playtest, I have looked on these threads and comments about how things need to be changed to match some part of a previous edition with bemusement. I do not have the experience of finding those mechanics that I really enjoyed and want to see continue. I imagine that if 6e dropped advantage/disadvantage, I would strongly consider house-ruling it in before giving the new system a try on its own.
That pondering aside, the thing that I am looking forward to bringing from previous editions is the stories. My table is going through a 5e conversion of Age of Worms, and we are having a blast. Between the published adventures, Dungeon, adventure paths and new 5e adventures, I think it is going to be a buyer's market for off the shelf stories. While I think my next campaign might be more of a homebrew (modified Spelljammer), I probably will still be using published adventures and one shots in parts.