It seems quite strange to me that hackers have adopted "0xdeadbeef" as some sort of generic hex string to use in production.

AFAIK, "0xDEADBEEF" originated as a "magic number" in systems like IBM RS/6000 and Solaris, and it was a red-flag number! It meant something in your system was wrong and you'd better check it out!

https://en.wikipedia.org/wiki/Magic_number_(programming)#Deb...

Surely there are more pleasant, vegan hex strings to use, if you want to indicate an ephemeral IPv6 address?