@Misadventure To me, seeding ideas is a combination of dropping hints and suggestions of things that may happen down the line; introducing an NPC who will be a big deal later, or dropping information that seems not so relevant now, until suddenly next week, someone goes OH WAIT.
It can also be bringing up new angles or different points of view to the existing -- inspiring players to grab a ball and run with it. I think the best example I've seen was a closing scene in a storyline I did in which the villain NPC was defeated. A supernatural creature, it was then brought back by another player and adopted as a guardian spirit by them -- which leads to all kinds of new shenanigans.
To me, a lot of this has to do with letting go of the reins. You throw balls up in the air; some of them get caught. Players think outside of the box, do things you had not expected -- you grab those balls and run with them. Stories never turn out the way I expect and that is part of what keeps me entertained. Nothing like planning a big epic fight, only to have the gang shame a sixteen tons dragon into slinking off like an embarrassed puppy.
On the official metaplot/staff-run things: I tend to run pretty parallel because that way, I can do what I want to do without needing to coordinate closely (this is a big deal for me since I'm in European time and having to wait to talk to someone in PST will literally slow everything to a halt for 24 hours or more).
I also enjoy doing what I call ambience events -- we had a major storm of the century plot on Gray Harbor recently, and during that, I ran stuff in a hurricane shelter. So, related to the official story, but not so closely tied in that I lock anyone in anything.