It is a huge security hole. The problem is that people are using v4 all over the place as a source of “unguessable” tokens. This is not the purpose of a UUID an

It is a huge security hole. The problem is that people are using v4 all over the place as a source of “unguessable” tokens. This is not the purpose of a UUID and is wrong of course, but it doesn’t change the reality that many services will become vulnerable if they change UUID schemes.