Just throwing this out there- you can pretty much prototype this, and a whole load of different layouts, with a couple of Dumang DK6 boards placed next to each other (if you wanted a single board instead of a split). Though the up/down arrows and F7 would have to be slightly off to either side.
Yes, I've seen that and it's a great idea and implementation, but availability, pricing, shipping/importing can be problematic, especially in my corner of the world.
But in order to prototype a design you don't really need to get too fancy. You can export the image from KLE, print it in 100% scale, glue it on a foam board, stick the switches on it and type away. I would encourage anyone even a little interested in ergonomics or/and keyboard design to give it try. Float your arms in front of you in a comfortable position, keep your wrists straight and fingers relaxed and track the natural movement of your fingers onto a board. You'd be surprised at what you'd be able to discover and figure out how even popular "ergo" boards (there's one that slips my mind right now, starting with "AL" and ending with "ICE") are actually pretty poor designs. You could try the same on a small one-piece ortholinear keyboard and you'd probably arrive at similar conclusions.
Also, high-speed video recording seems to be a common feature now on phones. You can point the camera on a specific area of the keyboard, type for a little while and watch in slow motion how you press the keys. This is why I added the gaps to the keys pressed by the ring and pinkie fingers. I noticed that I was consistently pressing those keys way off-center.
Finally, to go a bit on a tangent, some years ago when I started learning about keyboard design, I always assumed that row staggering is bad and ortholinear is good, but that's not universally true of every design. If you don't want to rotate the two halves (split angle) you can, symmetrically, row stagger the keys and that should get you part (most?) of the way there.
For instance on a standard keyboard, the row staggering on the right side helps align your hand with the keys, but of course it does the opposite on the left side. You need to twist your left hand unnaturally outwards in order to hit the reverse staggered top row and this is why touch typing lessons teach pressing "c" with the middle finger instead of the index. This is also why stepped caps-lock keys were introduced. With a twisted wrist, an overextended pinkie fans out further to left, causing mistypes. A stepped caps-lock is really a band-aid solution to serious design flaw.
My inspiration for this design were the Esrille, the NEC PC-9801 and the NEC Ergofit and only when I started testing their design choices, I appreciated and understood their elegance.