Title says it all.

U32<NativeEndian> is a real mouthful, and working around it by including type NE = NativeEndian; in each file it gets used in would be really unfortunate...

If I had to guess, the reason this doesn't exist yet was because it might lead to confusion with NetworkEndian? That's just a guess of course, but in case that's right: I don't think it's too confusing, given that the Rust standard library already has the convention of implementing methods in triples of be/le/ne (e.g: uXX::{to,from}_{be,le,ne}_bytes())