I'm in camp "arrows on hjkl on a layer, home/pgdn/pgup/end right below that", but if you really want them as physical keys, I'd probably stuff them below the pinky cluster, right next to the outer thumb.
That, or maybe something dpad-like on the left edge, close to the H.
Edit: Oh, for clarification: I'm a programmer, as well. I make plenty of use of the arrow keys, so it's not like "eh, let's stuff those on a layer, I never use 'em anyway" or something.
If you put the arrow cluster under a layer, you could use the right hand thumb cluster + one key on the bottom row. The layer could be activated by a left hand chorded keypress.
I understand what you’re saying, but what I hear is “I want unitask keys that only do one thing, and are objectively harder to reach”. To me this lessens the effectiveness of this sort of build.