It's funny looking at the reaction to rain on iRacing. Most people enjoy it, but there are a decent vocal minority on the iRacing forum that hate it whenever it's used. I personally love it on iRacing, but for LFS I think it's the very last thing on a very long list of other possible additions.
A well implemented rain system took iRacing, with a dev team of many people purely focusing on rain, many years to complete, and it still has elements missing from it. I think if we asked Scawen for rain and he fully focused on it, we wouldn't get any updates for years.