It's neither a new idea nor an unusual one. Many MMOs have dabbled with it but few, if any, have gone as far as to synchronize weather effects with changes in the broad mechanics of gameplay. FFXI has an arcane system of crafting and synthing that no-one really seems to understand, in which the day of the week and even the direction you face may, or may not, affect the outcome. That's coming from a similar direction but it's still not weather.
For the most part you can ignore the weather conditions in MMOs. If it rains your character won't get wet. The dirt track he's running along won't churn into viscous mud that sticks to his boots reducing his movement speed. Those thick eyebrows you were so proud of at character creation won't soak up rainwater like a sponge, dribbling it down into his eyes and knocking twenty percent off his Precision skill. That gleaming, two-handed spear he loves to carry strapped to his back like a flagpole won't attract a lightning strike that hits for 2k points of electrical damage.
I suppose it's a bit rich to expect environmental causality in a world where a three-foot high gnome can swim ten miles across a lake wearing a full suit of plate armor while carrying six backpacks full of iron ore. There's that oft-cited realism vs fun dynamic to take into account after all. Still, when asked, players generally seem to be in favor of some correlation between what they see on the screen and what's happening to their character and it doesn't seem to be beyond the wit of games developers to incorporate at least a modicum of entertaining cause and effect.
They certainly seem happy enough to include specific, localized environment-related gameplay when it suits them. GW2, for example, currently going gung-ho for sandstorms, has a number of places where crosswinds blow, strong enough to knock your character off a ledge to her death or at the very least the start of a long clamber to get back up for another try. Rift has a "dungeon" where white-out blizzard conditions form a major part of the final challenge. Many MMOs have lava pits and flows that cause burning damage (I seem to remember one that was instant death). Both Vanguard and WildStar have rivers with currents that will move your character against his will in the direction of flow.
All of these, though, are primarily environmental effects, not weather. When it comes to large weather systems that affect large areas or entire maps the only reliable impact on gameplay comes not from changes to the in-game mechanics but from a simple, practical fact: if you make it hard for the player to see what's on the screen the player will perform less well.
The history of blanking out the screen to make things more "challenging" goes back at least to Everquest. Back in 2000, when the rain came down in West Karana I used to have to go and hole up in the Centaur village 'til it stopped because I quite literally couldn't see far enough to know whether I was about to walk into a lion. When the Kunark expansion arrived and I ventured into Firiona Vie on the first day, the combination of thick forest, pounding rain and deadly wildlife meant my druid lost her corpse for good and all as did the couple of people who bravely helped her try and find it.
Rain, snow, mist, fog - they all work to disorient and constrain the player. Add in a proper day/night cycle and you can render many of your outdoor zones nigh-on unplayable more often than not. For some reason players didn't seem too enthusiastic about that so over the years night became twilight and twilight became a tint in the filter while rain, snow and fog ceased to be brutal gamestoppers and developed into delicate, beautiful visual haikus.
In so many ways this is a good thing. For a start, the sheer, breathtaking beauty of the weather in modern MMOs creates a weather-high barely less powerful than being outdoors in actual weather. On these hot, sultry summer days just looking at the Shiverpeaks drops the temperature in the room.
Then there's playability. The first few times I got caught in a rainstorm in EQ it was immensely affecting and immersive and the first time I got lost at night, an old story often re-told that I won't rehash here yet again, it created a deep and lasting memory that endures vividly to this day. Just a few weeks after those seminal experiences, however, impenetrable darkness and rain that reduced visibility to a few yards didn't seem so immersive any more. They just seemed irritating.
The pendulum swings. The roundabout turns. Perhaps the days of meaningful weather are due for a comeback. On balance I hope so. I wouldn't advocate a wholesale return to the days of "sever weather conditions expected - stay indoors" but I think there must be ways to have our characters recognize the impact of cataracts and hurricanoes without making players rave like Lear on the blasted heath.
If H1Z1 gets it right perhaps that will pave the way for meaningful weather in EQNext or even Landmark but as Renee Machyousky, Community Manager for City State Entertainment, producers of the upcoming Camelot Unchained, observes in reply to a question about the influence of "day/night cycles, weather, seasonal influences on game play", it's a balancing act that all developers have to perform with extreme care:
" ...we need to find that sweet spot where we implement just enough of them to keep people engaged and entertained, without feeling overwhelmed or worse, frustrated".
Agreed, but I think that sweet spot is somewhere a little saltier than where the genre is right now.