I was going to reply about the times I've had missions go easier because of rain (being able to shoot tires more easily and spin target out, waves slowing down target boat etc) but now that I think of it those aren't dynamic those were all scripted. Even in GTA V for the main story missions it sets you in specific mission parameters as the mission starts which includes the weather, like when it rains at the Lost funeral for Johnny's chapter.
It would be an interesting concept if they could do it, and I'm sure with it being set in Miami a hurricane or tropical storm will feature at some point in the storyline, or at least I hope it would. If they could add dynamic weather so that, say, fog could make a heist easier or a popup rainstorm could make for a trickier getaway, that'd be cool. My hopes were set high with games like Battlefield pushing big weather and stage effects and it's like devs just lost interest.
I've watched the trailer a few more times and one thing I am really struck by, other than the demographics, is that the body physics look fucking amazing. Like better than I was expecting even after 10 years. If the physics work like they do in the trailer it's a huge step up because the movement all seemed very fluid rather than the stiff legged jankiness that was in V.