I'm honestly unsure why we can't already. They use the same animations (amplifier looks a bit silly with one handed weapons, but it's there) so it's really just a cosmetic thing? Probably how the game checks if items can be glamoured over each other? But then the items that glamor over multiple slots/vice versa can be glamoured over eachother? Are one and two handed weapons handled differently than those other items slots?
Either way, yeah it'd be nice.