Zones where it like always rains, and when you get closer to say HNM spot, or closer to an evil dungeon, or closer to a higher level zone/area... the rain turns to blood or some other different color. To signify you're nearing something. Maybe the rain can even just change direction, to show the weather is getting worse.
Say as we got closer to Dzemael Darkhold, the sky just got dimmer, and rain started, but when you're far enough from the zone line, the weather goes back to normal.
Like the plains in FFX, a zone with all lightning weather, and every so often the ground starts to glow to signal a lightning bolt is about to crash in that perimeter, like eruptions from ifrit, but, more/less reaction time depending on whether we lose animation lock or not. Getting hit by lightning can take off % HP or something, maybe there can be specific gear or buff that can be cast to negate lightning dmg (or SS can eat it).
Snow weather, and as you get closer to HNM/zone/area the blizzard can pick up, standing still for too long in certain areas, or this area in particular can give you some frost debuff idk.
Dark weather (not purple) where it's like night time or the skys dark, for instance clouds block out the sunlight all the time. So it's never really bright. It's just like being in a shadow zone. With only lights/lamp posts to guide adventurers... Maybe have some tough monsters who make loud noises hiding in the shadows of places players shouldn't wander off too. Additionally there could maybe be some little glowing bugs that hover around and they're the only source of players able to see certain areas of the zone. Either way, the general concept is a dark ominous zone, like Castle Zvahl Baileys + Castle Zvahl.
That's from Amnesia, but having say 1 little zone where players feel like they're playing a survival horror, and the monsters are from demon mythology or w/e... The zone can lead to Count Draculas castle or something.
Lastly I thought the Dynamis zones were pretty cool. There was obvious differences from the cities in Dynamis compared to the regular version. Perhaps having like a high monochromatic zone/weather color. Not completely black and white, but very faded, like the zone is taking place in the past...
Fighting in a city would be exciting, like a lost/forgotten/pillaged city, the size of Ul'dah or something. Only it's riddled w/ smoke and fog, and there are flames scattered everywhere.
Really don't expect any of these to ever be implemented. Just my expectations for a revolutionary MMO. Though 11 allowed players to deal extra elemental damage during that elements weather/day, I don't know how many other MMOs had similar/unique uses for their weather.
And Dodore during purple weather is another good example!