Got to admit that after these few days of compare shots across quite a few mods, then it seems that unless something is essentially just a rescale then it is not good enough. For the next version of the guide I think we should have a debate on getting a more clearly defined "acceptable style change"... It makes no sense to expect that talented people just do rescales of vanilla any more.
Also I do not agree with your apparent definition of "vanilla friendly" in this case... I would say this mod is VERY vanilla friendly! There are not radical design changes... I still find that this mod blends in nicely with other dwemer textures.
That said then the size should really not be a relevant issue... it is always far better to have a base file of high quality then alter the compression and size manually. We do it for just about every texture.. so I fail to see how this is an issue. Also 2k for an enemy model.. that is mainly only present inside interiors... even smaller laptops would not have a problem with that since the interior memory requirements are so paltry.
Hope that all made some sense hehe!
Style changes are already covered in this statement on the Mandate for Core under what it is NOT about: "... mods that subjectively alter or contrast with the style of vanilla Skyrim."
Besides the hi-res texture, all of the changes here are subjective. Color, contrast, tint, brightness, etc It's all the authors vision, not the direction that Bethesda set for vanilla.
This could be tested for Extended as long as the change in that stone color doesn't contradict anything in lore about the stone suppose to being red (power source, etc).
I do suppose we could discuss how ridge we want to be because there are some mods in Core that changes the "shade" or "contrast" of some colors; however, nothing in Core makes complete changes from, say, red to purple.