While symmetry is a good thing, and this layout is nice, I don't think the navigation keys in the middle will work well.
Most people access the navigation keys (arrows) with one hand. Of course this may just a habit come from old boards putting these keys in the right hand side. However, this middle navigation keys will lead to two possibilities:
1) one has to move one hand to access theses keys
2) one learn to access these keys using two hands
The first will affect the typing since the hand will move between the home row and these navigation keys constantly. I am not sure about the second, but I imagine some editing works will become much more complicated.
Perhaps these keys can be assigned to other functions, and accessing the arrow keys with some function keys. For example, I have assigned my 'f' key to a layer switch, while I press this key, 'jkl;' in the other hand become the navigation keys. This way, my hand do not need to move all the times.
Also, the positions of the space keys will cause the thumbs to move inward, which might cause some strain. Perhaps you can merge the 'left' and 'right' keys with either space key. This will lead to more natural typing.