When you see Rogue One: A Star Wars Story this year and Star Wars: Episode VIII next year, you might be able to catch a fun cameo if you're eagle-eyed enough. Director Gareth Edwards and writer/director Rian Johnson had some overlap in the production of their respective films, and when each visited the other's set, they decided to trade cameos in their films, Johnson revealed at Star Wars Celebration Europe.
In Rogue One: A Star Wars Story, we'll see the group from the nascent Rebel Alliance that forms to steal the Death Star plans and jumpstart the rebellion. Well, as you may have guessed, that means we'll see the Death Star itself, in all its glory. Johnson chose a key member of its crew as his cameo, and may have dropped a bit of a minor spoiler. When he described his cameo as one that's impossible to be cut from the film, he may have revealed an event in the movie. "We're each one of the guys in the firing chamber of the Death Star," alongside his assistant, and he said he would be "pulling the lever." That seems to imply the Death Star is fully operational, and would be firing its signature blast. Johnson will be a bit hard to recognize, of course, as he'll be wearing one of those ridiculous upside-down-Wok black helmets during his screentime.
For Star Wars: Episode VIII, Edwards' cameo was a little less momentous, merely being some sort of technician or townsperson - they didn't want to reveal it too specifically for fear of revealing a story point for the film that's still a year and a half out from release. The panelists did joke, however, that the creature effects pulled off in the picture of Edwards on set were "simply amazing!"
As for Phil Lord and Chris Miller, they were actually completely costumed up for a Rogue One cameo set on Jedha, one of the new (and very mythically important) planets in the film. Unfortunately, before they could shoot, they had to leave the set to look for schools for Miller's son during his year of living there while their untitled Han Solo Star Wars Story film is in production.