Even though the next non-licensed Pirates theme is 2-3 years away at minimum, it's still possible to speculate on how the new parts, innovations and building styles of today might affect the future of the theme. With the reviews for POTC Silent Mary just coming out, I thought that would be a good place to start.
Weaponry: The previous POTC sets all had the classic brown guns and rifles, but the guns in Silent Mary are all pearl dark grey (or something similar). It could just be a new look specifically for Silent Mary and/or any future POTC sets, but it's possible that, after 28 years, grey guns are going to be the new normal.
Headgear: The 2015 Soldiers didn't have tricorns, but the ghost soldiers on the Silent Mary did, so I think it's entirely possible we will see tricorns on the soldiers again in the future. Also, I don't see why we wouldn't see the balding bandanna look from the Scallywag Pirate used again, maybe in other traditional bandanna colours like white, blue and green.