This is now well into A380 territory.
I think that this is more of a failure of management than engineering. While the extensive use of composites is new for a civil aircraft, as is the “all electric” nature of the accessories, the degree to which Boeing has outsourced basic engineering and designs to so-called “partners” seems to be a much bigger part of the delay.
First flight is not in Q4 of this year, and if it’s before December 15, I will be very surprised.