Hi,
I am the author of BetterUI and my goal for this addon is to make the interface as usable as the keyboard interface is.
Here is a sneak peek into the next (large) update to BUI. It is still VERY much in testing and designing at the moment, but I have altered the inventory interface extensively.
My inspiration for BUI was from the Skyrim mod SkyUI (which is the screenshot you attached) so we seem to have a common goal!
I have yet to implement the "horizontal" aspect of category picking, but that will be put in very soon, probably in the next few days
