You need to enable deferred pre-pass in the shader settings to make it work in deferred

I'll have to look into this after GDC I'm afraid, but thanks for the detailed report!

You can use two cubemap nodes, plug the gloss (remapped from 0-1 to 7-0) into the MIP input of the cubemap, and then plug them both into A and B of a lerp node, and a slider in the T input. Then plug it into the specular ambient light input.
Otherwise, blending should work as it is, if you're using Skyshop's built-in one.

No idea what could cause that, and it sounds more like a Unity bug rather than a SF bug :/

In the update loop might do. myMaterial.SetFloat("_MyTimeProperty", Time.time);

Good question. Looks like the time variable is losing precision, either because the number is too large or too small.
You might need to push in a time variable yourself using myMaterial.SetFloat()

Which is exactly what you can do using the texture asset node :)

You *have* to use the Texture2D node multiple times, there's no way of "moving" a sampler other than sampling again at another location. Look at the page you linked:

sum += texture2D(RTScene, vec2(vTexCoord.x - 4.0*blurSize, vTexCoord.y)) * 0.05;
sum += texture2D(RTScene, vec2(vTexCoord.x - 3.0*blurSize, vTexCoord.y)) * 0.09;
sum += texture2D(RTScene, vec2(vTexCoord.x - 2.0*blurSize, vTexCoord.y)) * 0.12;
...

each Texture2D(...) is another Texture2D sample node :)
Simply connect the same Texture Asset to multiple Texture2D nodes, and use different UVs, then sum them up

Glad you find it useful, and glad you found a solution for now! And yes, there really should be a face-sign node, but right now I'm a bit swamped in other work I'm afraid

Not yet, my schedule is unfortunately completely full until after GDC

I'm not sure what you mean - you can't "change the UV after the fact", you have to sample it again in that case, which is what the Texture2D asset node is for!