The Meaning of Life, the Universe, and Everything.
In another voxel game.
That other sandbox game.
I have nothing against the idea but... Here's the thing, it almost seems like Mojang itself loathes the idea of two hands... And I kinda know why. This isn't the first idea like this, and there are quite a few mods that do this so Mojang can easily adopt this and clearly get a good amount of support for it, but there's something else at work here.
Unlike pistons or carpet or stained glass, this is almost controversial. People take a bunch of different sides on this; for, against, this way, that way... While your idea is indeed balanced, it will still have the pugilists and swordsmen alike fueding and bitching about how it works. This idea can't please everyone, and Mojang-crosoft... doesn't like that. It's a good idea, but the time tested truth is that we will always be amputees in Mojang's eyes.