Hi, I have done some searching around on UE4’s website and found out that there is only one workaround for parametrizing the UV channel index. It is achieved by creating a parameter switch node that switches between 2 different UV channels. IMO, this sounds silly, since sometimes you want to use the same texture on multiple objects, such as a texture sheet, but each of them could have 2 or more UV channels. Having that many switches seems over board, which eventually would boil down to not making a texture sheet and create separate materials for each object. Either way, this creates to many instructions for something that uses the same texture. The whole purpose of a texture sheet is to able to use one texture for multiple objects, based on where the UVs are placed in each object, but it should not restrict designers from using the same UV channel for all of there work.
Also, while we are thinking about this, it would make sense if the U and V coordinates can be exposed. Up until now, there are only workarounds for manipulating the U and V coordinates as well. For example, tiling the same amount for the U and V coordinates, the texture coordinate node needs to be multiplied by a scalar. However, it gets more complicated when you need to change the U and V coordinates with 2 separate values. Its workaround is to separate the U and V coordinates, makes your changes, and then the U and V coordinates have to be appended back into a vector2 node again. However, by exposing the coordinates in the UV coordinate node, this will allow designers be able to make there changes and plug them into their respected pins without having to worry about separating and appending vectors back together again.