The horse-riding gameplay we've seen in Metal Gear Solid V's trailer is just too much for ArmA III and its engine to handle. But sacrificing realism in order to remake the original trailer perfectly in a completely different environment is a good idea: It will make everything and everyone look silly.
Here's YouTuber rebelvg's remake. Metal Gear Solid V in ArmA III. Definitely a lot of effort was put into this.
Metal Gear Solid 5 Trailer - Arma 3 Remake [rebelvg, YouTube]