First off, this is a truly great idea and fantastic mod. I love what's implemented so far and look forward to further developments.
I noticed that up this thread a bit someone mentioned the possibility of doing some sort of check so that you wouldn't hear rain (and presumably other weather) sounds far deep in a mine (or otherwise far underground). I don't know how easy/difficult this may be to implement, but so far it's the one thing I noticed that seemed really "off." Having weather sounds is fantastic (and really helps establish ambience in the world), but it's a little odd if you spend a couple Minetest "days" far underground digging and in the middle a storm comes up and you get rain sounds for several minutes.