From the video it looks like it takes more from Arc and Monster Hunter than it does Horizon. But there's definitely Horizon flavoring with the giant machines and such.

But I mean, a combo Horizon, Arc and Monster Hunter does seem like a good idea.

Maybe not for an MMO, because other people tend to ruin things, and the inevitable grind and daily log ins, and in game shop, etc. But for something like a co-op game with those three flavors, heck yeah.