It is definitely messy to deal with large node trees at the moment

I would prefer to have one request per topic, so, I'll ignore the zooming in this topic.
Zoom has already been requested, as you know, and is one of the top-prio things I'll look into. (That said, I have looked into it several times and had issues getting it to work. It's a big time sink)

I have thought about two ways of disabling node previews. One way would be to collapse them to smaller icons instead of visible textures, and another would be a checkbox to simply not recalculate them, like you said. For now I'll go for the latter.

It is, however, sweeping the problem under the rug. What I should look for is a way to calculate them faster :)

A Normal Blend node is now implemented in Beta 0.23 :)

SF is already using Cook-Torrance in the PBL mode, though it's not using Oren-Nayar diffuse.

You can use shift + space to toggle maximize on windows in Unity

I think I'll decline this one, as it seems a bit OS specific and depends on how Unity wants to manage their windows. It's probably a good idea to stay consistent.

That said, you can put SF in another tab, and switch back and forth :)

This has now been implemented in Beta 0.23 :)

Here are the 18 ones implemented:
- Darken, Multiply, Color Burn, Linear Burn
- Lighten, Screen, Color Dodge, Linear Dodge
- Overlay, Hard Light, Vivid Light, Linear Light, Pin Light, Hard Mix
- Difference, Exclusion, Subtract, Divide

Here are the ones not implemented, if you find any of these important, open a new topic:
- Normal (We're not using alpha, so this mode is redundant)
- Dissolve (We're not using alpha, so this mode is redundant)
- Darker Color (Same as Darken, but based on color luminosity)
- Lighter Color (Same as Lighter, but based on color luminosity)
- Soft Light (Rather complex and expensive to use on a shader level)

I think you first need to figure out how you want to combine them.
The RGB outputs of the textures doesn't have the transparency data, so without using those in some way, they won't deal with any transparency.

I presume you want a photoshop layer-like blending, in which case you can simply use a lerp node instead, and connect one of their alphas to the T input :)