One AME's opinion making the rounds:
From what I can see, no significant portion of fan is missing, all components affected are forward of the fan. We've seen early indications of this sort of thing and it is something I've been watching for for some time but until now have yet to see it this bad.
When metal work ie. repairs/patches, are done on the nose cowl, frequently rivet ends, tails and other swarf are left behind, inside the nose cowl. The nose cowl anti-ice air swirls these bits around abrading the inside surface of the cowl - counter clockwise when viewed from the front looking back, from about the 8:00 position. The worst damage is from about the 7:00 to about the 1:00 position.
I have seen where all the rivet bucks and a significant portion of the skin have been eroded away...to a significant percentage of skin thickness. There is no external indication until a lot of the rivets at the aft end of the nose cowl are loose/smoking. Any cowl that has been repaired with blind fasteners, particularly repeatedly, could potentially have very hard cherry pulls (blind fastener components) left inside the cowl. When a nose cowl is removed/replaced, the interior is still not visible and it would be unusual (until this) to look in the locations I'm talking about. These locations are only visible when the cowl itself is disassembled. In my opinion an over-pressure of the nose cowl is highly unlikely due the size of the vent for that air.