I know A LOT of people would not want this, but I feel like Mashima's new work might continue into the Fairy Tail world. There are loose ends that weren't tied up (Aquarius's key probably being the biggest one), and it could be addressed in his new work. It could be a timeskip, like how Naruto did Boruto.
Honestly, I mostly just want this cause I want to see concrete Nalu. I stopped really caring about the plot a once Natsu woke up from his coma and said he wasn't END anymore because he chose to be human. If there was one thing Mashima was good at though, it was making me care about the characters. So after all those Natsu and Lucy teases and the trolling, we get THAT?! I'll admit I was angry and severely disappointed.
But nonetheless, despite my gripes and the admittedly lackluster writing, it did what I want a story to do. Make me care about the characters and what will happen to them. It was a great ride and I'm genuinely looking forward to Mashima's next work, whatever it may be, Fairy Tail universe or not.