Joachim, please forgive my ignorance here but isn't it as simple as:
float3 node_# = DecodeLightmap(tex2D(unity_Lightmap, i.texcoord))  ?

Or maybe you don't have available interpolators at this point to pass the texcoord in?

Hey there, I know it's been a while but I just wanted to see if this was still in the works?  Also my original request specified the lightmap being a node... it doesn't have to be (at first), just being able to check the Lightmaps support while also using Unlit/Custom would be great.

Having a lightmap node would still be fantastic though for doing custom manipulations on the lightmap right in the shader.

I use ShaderForge extensively and this would be a HUGELY helpful feature.  My shader graphs can get pretty complicated (and I try very hard to keep them organized and nicely spaced/aligned) and if I revisit them after even a few days of not looking at them, it can be difficult to remember what connects to what, as I'm constantly adding/removing node networks but sometimes keeping them off to the side "just in case" I want to plug them back in.

Being able to clearly see what I am currently using would save me a lot of trouble of having to read through the networks and reverse-engineering what I already plugged together days or weeks ago.

How/when it shows up, I'm not too sure.  I like the idea of clicking on the line to turn the highlight on, and then clicking on it again to turn the highlight off.  I don't think I would like it to ALWAYS display, nor would I like it to be on mouseover since now you'd constantly have highlights turning on/off as you navigate the shader.