The big question though is why was this needed.
Texture changes can sometimes be very much needed, such as the Buildcraft change.
However, the texture change for Mekanism (and Blood Magic in 1.8+) is too much, too fast.
If you have a new mod and are trying to work on functionality, then make better textures down the line, then that's fine. However, the changes to Mek were not all that pleasant and really changed the aesthetic of the mod. Also seeing as Mek has been around for a while, changing the textures really screws up with the instant recognition of items when you open a chest.
I still love Mekanism as a concept, but I really do wish the textures would get reverted.
If the textures didn't get ruined in this update, then I could overlook a few changes which broke some parts of the mod (e.g. couldn't craft the armoured jetpack - in 9.0.0) and the little changes which are so-so, like the amount of carbon/redstone/etc. you get from the compressed variants.