It would be cool if servers could use real-world weather station reports and set the in-game weather to match. This would give a more realistic simulation of type and frequency of weather conditions.
If each server could choose its own real-world weather station, people could play on servers that use their local weather, and when it's raining outside, it'd be raining in DayZ too.
With the numerous online sources for weather reports, it seems like it would be fairly straightforward. Flight sims have been using real-world METAR reports for like 15 years now.