I don't think it's a tantrum or vengeance scheme because I doubt SE would agree if it was nor do I think it'll be them making a VsXV because I don't think SE is going to do another big project on that world anymore. Like maybe they're just all having a laugh and ribbing everyone with this lolThe ending is not a fuck you to anyone. It's a tantrum.
XV is already released, and in Square's eyes it was a massive success, and the fastest selling Final Fantasy to date. Square has no reason to make a do-over for this game.
Nomura doing this affects no one. But it makes seem vengeful and childish.
If it was only the looks and part of the concept it would be fine. But the whole "Verum Rex" and the reuse of Somnus as musical motiff is taking things too far.