Yo, got a few question and thoughts about the subsurface scattering updates 
Having a Subsurface and a Subsurface Scale slider feels like both of them are doing the same thing, except they are not. From my small testing the Subsurface slider sort of “fades” between whatever subsurface you have to just a default diffuse shader, while the Subsurface Scale slider actually scales it in a more physically correct way. Is my assumption correct? Because if that’s the case I think it should be more clear somehow what slider one should use if you want a more physically correct material.
It kind of feels like the Bump node where you really shouldn’t use the Strength slider since it just “fades” between full bump and no bump which is not the right way to do it, it just looks bad no matter how you arbitrary change that slider, and unfortunately almost everyone still uses that slider because it’s labelled in such a way that people think that’s the one to use (and also since you generally have to set the Distance to very low values to have any real effect since this value is in meter (which is not really clear either)).
And about that radius, this might be nit picking, but shouldn’t the input be an RGB one since that’s what you essentially is just multiplying the scale with in there? I mean if you change individual channels you clearly see that it is R, G and B that you are changing, not some X, Y and Z coordinate. I mean the way I use it is to just plug in a RGB node which I feel makes way more intuitive sense.
I also have a more general question about the three different SSS implementations.
Often when I use SSS I have objects that are different shell but should still act as one, so the only option for me there is to use Christensen-Burley. Not sure what the different options do under the hood, but is it possible to have all three of them being able to “melt” different shells together like this, with maybe an option to turn this feature on or off?