There are many interesting ideas of how you wanted it to end, but it's not really how it should've ended, it's more like how you wanted to end.
Why did the Fairy Tail suddenly made Wendy the main character to kill that one ultimate villain in the manga?
But I did wish there was an actual Etherious form of Natsu, but not just him all along, it loses control and the fairy Tail tries to save him using Nakama Magic.
Again my personal theory regarding Mavis and Zeref is that their curse was never lifted, they both wanted to die, but still they're alive, reincarnated.
Wish August was alive. wish he didnt die in the most ridiculous way.