
Default layer -

Extend layer -

Num Lock layer -

Function/Space Fn layer -

DEFAULT layer
This will also be available in Colemak.
The beauty of the Katana60 layout is that pretty much every key is accessible via the home row, but there are still a good number of 'spare' or harder to reach keys which can be used as one-shot hunt-and-peck keys. Eg, in my personal layout, I use the media controls (found in the Extend layer) in the middle, instead of the navigation cluster (home, end, page up/down etc).
Of course it is possible to use a 'traditional' arrow cluster arrangement (bottom right) or the central location (as in the original post). The firmware is based on QMK, so its fully customiseable.
EXTEND layer
Currently under development over at the Colemak forum. I'd say the right hand is nearly there, and the left hand is subject to changes before launch
NUM-LOCK layer
This could be shifted 2 steps over to the right, so the numbers 4, 5 and 6 align with the hand in the home row position, I just like the fact that the '0 Ins' and 'Num Lock' keys line up perfectly for this position!
FUNCTION layer
I have been using the space key as [tap = space, or tap-hold = functino layer modifier], some may prefer to remove the layer modifier option. In this case I would suggest moving the Fn key (currently on the bottom left of the default layer) to the middle of the bottom row (where the shift key currently lives). Then you'd have a space key on the bottom left

Please let me know your thoughts on the above, I'd love to hear your feedback.