It seems to me to be an amazing amount of damage for a bike/frame that has not been in an accident. I'd hope that Kawasaki's rational for fixing this out-of-warranty is a combination of goodwill as well as genuine interest in having the broken frame back for analysis. As others have noted, this is a very rare happening even for a crashed bike. I know if I was an engineer at Kawasaki I would want to know what happened here. Was it bad materials, bad manufacturing, or something that happened to the bike after it left the factory.
What you note above, is EXACTLY why Kaw was interested in covering this repair, they are a very complete and technically astute company.
As a Mechanical engineer myself, that has worked in both the consumer product industry, and also Military, Nuclear and Defense Industry, and extensive welding and fabricating processes, I can say without a doubt the first issue Kaw want's to address, is going back thru records of all the parts and assembly, with special regard to all automated welding that occurred, and the materials used during the period of manufacture. This stuff, even tho most don't realize or believe, is extremely well documented within the manufacturing infrastructure. Raw materials, both used in cast parts, and machined parts, spools of welding wire, etc., along with periodic non destructive testing that they actually do, is all recorded, and each part fabricated has a paper trail, or should I say a bar coded electronic record trail within their system.
Even something as 'invisible' as a malfunction on the automated welder, if the 'shield gas' was not present due to a malfunctioning valve... would have popped up on the controls, and been corrected; so there would be a record of that occurrence.
I mention that particular part of the welding process, because I have seen this happen before, when incorrect or lack of correct "shielding gas" was not present during the welding process, which resulted in structurally unsound welds, even tho visually (via UV Mag-Flux), and ultrasonically(no porosity contaminants seen) the welds appeared fine. But during microscopic analysis of the cross section of the weld, and chemical composition, the grain structures of the weld components could be seen as root cause
Now, they will do in depth NDT, Ultrasonic, X-ray, and chemical analysis, of that particular failure; and determine the root cause. Been there, and done that myself, when I worked in defense critical products and structural analysis.
It's all for good tho, and behind the scenes, they will compile a "list' of all the possibly effected units in the field, and issue 'silently' send a notification to those possibly effected (like the bike produced from that week prior, and after) the suspect part was installed on.
I'm just glad the dealership actually took this seriously, and persistence resulted in a good outcome for all concerned.