It will be a desaster.
He wants (or needs) to finish it asap, but that simply doesn't work with the current setup of the story at all.
You can't write an ending in 5 years (aka around 160-180 chapters), when you literally have to target and explain every single (!) endgame plot-point, bc you didn't do so before, and also already wrote almost as long arcs with tons of irrelevant goof-chapters.
I mean he probably will do it, but explain to any objective fan how a 160 chapter final saga (Elbaf, Laugh Tale, BB final fights, war against the WG) can be satisfying, when you know that even single arcs like Dressrosa took 100 chapters or Wano right now with its 150 chapters and a ton of chapters wasted for unnecessary content.
People will ask where the relation is.