When Capcom shows this at Sony's E3 conference, if they want it to become a big thing, then they need to make a case for it. Cause here is something that MH fans might not consider/think about.
You say that MH has a vastly superior monster hunting and gameplay system than games like Witcher 3 or Horizon, and you might be absolutely right about that. I haven't played a MH game myself so I can't really judge. But the thing is, millions of western players already like those games even with their simpler monster hunting mechanics.
So, when they finally show this on PS4, the question for your average western player will be "okay, hunting monsters is cool, but what else is there?". Regardless of how much deeper the gameplay systems may be, the game will be compared to Horizon and Witcher and other games with monster hunting elements. And it has to have an answer for those comparisons, cause it needs to give people a reason to play this monster hunting game, instead of doing the hunting in a good amount of other games that are already available on PS4, and offer other things in addition to hunting monsters.
When that time comes, the game either has to have stuff like"amazing visuals", "interesting story/characters", "big open world with other stuff to do" etc, to be able to compare favorably against said games. Or Capcom/Sony need to make a very big deal out of how hunting monsters in this game is different and how interesting and fun it will be that just doing those will be enough for you to enjoy the game, without the need for all of those other stuff.
And I think selling the former would be much easier than proving (and risking) the latter.
Anyway, the point is that if they want this to be huge success on PS4 in the west, then I totally expect them to change a lot of stuff about the current structure and formula of MH.