Interesting. This the first time I've seen a pic from this angle on this stage of construction.
Obviously on a finished boat the whole frame is covered with the breaker panel with no hint of what's behind it.
At first blush, I'd say that wooden panel covering half of the opening is needed for support of the helm chair. A few inches of wood on the face frame over the top of the opening to the electronics panel would be a weak structure supporting a chair, hundreds of pounds of people, bouncing around in weather.
From this angle one cannot tell whether it is a flat board, empty behind it and open, or a box with an additional panel running side to side in the boat. It may well be a box, so that the unseen hypothetical panel could also provide seat support.
If in the end, this is an empty box that would be a first since pretty much every other empty cavity gets used by creating additional storage space.
This would be a question for Scott.