Rain/wet conditions definitely look a lot better. Would definitely help if you did longer Reshade OFF/ON comparisons though. Very promising tech here.
I don't think TSW supports it actually, there would have been an update from the devs. He must have turned it on somehow, don't know how as I cant even find it in Nvidia control panel
You need to pay $5/month to get access to Pascal Gilcher's Discord-server where you can download the shaders needed for this effect. https://www.patreon.com/mcflypg/posts
I noticed when enabled it gives surfaces a glossy effect. Does this happen all the time or only when its raining?
No. What you can do is join on Patreon, subscribe and pay $5, download the files and then unsubscribe before renewal. Not really, I have locked the FPS to 30 and it didn't drop below with the shader enabled. But my GPU-fan did speed up more than normal (GTX1080ti 11gb)
No. Shader is a program just like any other and it's developer deserves to get paid for it if he wants to. Sorry about that. It just bothered me. What is shown above is called "Screen space ray tracing" which means that it uses render passes (more specificly base color, depth and maybe metalness and roughness) to create the effect. Major difference compared to the stock screenspace reflection is that it has no roughness threshold which means that it computes reflection for all surfaces and not just these that are smooth enough. r.SSR.MaxRoughness=1 console command should create a similar effect but at much lower performance cost. I haven't tested it yet.