@Lambie I have never seen the word used that way.

@Lambie Please present evidence that ship means ‘to be in a relationship’. The ‘grammar’ here (whatever that is supposed to mean) is quite irrelevant. The meaning you suggest for the verb does not exist in any dictionary that I can find, whereas the well-known one of ‘desiring a relationship between characters’ exists in several. In a nutshell, the word has never meant what you claim it means. The fans do not want anyone to ship. That makes no sense. They ship them.

If the idea is that fans "have wanted them to be in a relationship", I would not write it as: Fans have shipped them. It's confusing.