EDIT: Somehow this became my original post. New one is below:
we need this because of speed. only that.
mPCIe has at least one lane (I can't find a definitive source), and that's plenty for most things. If you need anything faster, give it PCIe 3.0, for a GB/s each way.
Besides, who's going to put a GPU or similar on one of these? It won't fit and you can't deal with the heat.
When manufacturers must make thinner laptops its critical to get as many components as small as possible, so this is just one of many components that must shrink
So use a half-length one.