I've been using this keyboard some time, and it's close to perfect, but there are several things that could be still improved in my opinion, so I went ahead and re-designed the PCB a little bit.

I added a little stagger to the inner columns, because it was a bit hard to reach the T and Y keys. I also lowered the middle finger column a bit, because the stagger there was a bit much. The pinky cluster stays as it is, because it is perfect — I didn't even move it the 3mm needed to align it with the new keys.

I added a cluster for the cursor keys, because having them on a layer is not convenient, and I'm not touch-typing when I'm cursoring anyways. Since the board is by necessity symmetric, I will also have some extra keys on the other side — I will put the rarely used modifier keys there.

Finally, I added a place for a CapsLock LED, though I never use it. But there were free pins, so why not.

The layout will look something like this: