@Arkandel
In order:
Yeah, sure, that's fair. People need to be able to compromise. If Sniper Plot is important to me and you want to avoid it, I might do my best not to bring it up, but if it's at the climax and my character knows he's the next target, you're shit out of luck.
I think everyone who's running non-personal, game-wide plots should communicate. For Eldritch, I want to have a person on staff whose main job is to make sure people are aware of things that might affect each other's plots. It's gonna be difficult, but I think it would work great. It is, I think, essentially what @EmmahSue was hired on The Reach for, initially. In my example above, it's just as easy to have the runner of the Sniper plot page the runner of the Festival plot with: "Hey, would it be awesome if our plots intersected and the Sniper shot someone at yuour festival at a moment that affects your plot the least?" Communication is a two way street.
I think if one of the plots is being run by a staffer and the other isn't, it's still important for the communication to happen. The onus is only slightly more on the staffer, but only by a negligible degree. People shouldn't be afraid of paging staffers with stuff like this. A staffer running metaplot (as opposed to "regular" plot) should, IMO, always be on the look-out for how other plots happening can feed and be fed by the metaplot they're running. Lastly, if the plots are both being run by staffers, there's absolutely no reason there shouldn't be communication.
I don't really know what you mean with "precedence". If a plot is affecting things to that degree, it was probably either approved by staff or staff has looked at it and gone "we have no objections, carry on", which means there's no precedence-taking. It's all plot. At least, in sane games. There are always games in which plots are always crazy and contradictory, but if you have that as the default you have bigger problems in the "coherent narrative" department, anyway.