Very nice material on those rain drops, certainly better than in most games that have rain implemented.
This plugin is shaping very nicely, you have defenetly a winner here i think as long as you allow it to be scalable. If you can learn from other games sky systems such as Ark for example which uses True sky, the main problem there were the clouds which were tied to non flexible reducing of quallity which in end made majority of people have sky turned of completly, which afterwards make weathering a bit wierd (rain from clear sky and such). So keeping materials/clouds/systems scalable to settings is very important especially on those parts that are heavy hitters. Not trying to guide you how you should develop anything at all, just some observations from other games.