The trophy/achievement list for Monster Hunter: World has leaked a few days ahead of the game's release, and it indicates what we probably could've guessed: It's going to take a serious time commitment to get them all.
PowerPyx discovered the trophies list (achievements should be the exact same minus the platinum), and it indicates that nabbing everything will require scouring every corner of the world. There are a lot of cumulative-based tasks like earning a certain amount of money or hunting a certain number of different kinds of monsters. There's also one for reaching rank 100, which is presumably the highest rank possible.
However, it's the crowns that are the most intimidating. Monster Hunter's beasts all have randomized sizes each time you encounter them. If you're lucky enough to hunt one that's at the extreme end of the spectrum (either small or large), you'll earn a crown for your guild card.
Two of the trophies make use of the crown system. They're acquired by "Obtain[ing] a miniature crown for almost every monster in your hunting log" and "Obtain[ing] a giant crown for almost every monster in your hunting log." There will likely be 50-some monsters at launch (the final number isn't confirmed yet) and seeing these variations will rely entirely on RNG. It could take a very long time.
Here are all the trophies/achievements for Monster World: Hunter:
via destructoid https://www.destructoid.com/monster-hunter-world-s-platinum-trophy-is-going-to-be-an-ordeal-483908.phtml