Funnily enough, I had a quick look at the Cloudpost deck that made the Top 8 of the very first Modern Pro Tour in Philadelphia back in 2011, and the deck contained four cards that are now banned Cloudpost, Eye of Ugin, Green Suns Zenith and Punishing Fire
Its extremely versatilesometimes it protects your creatures, sometimes it removes blockers, and probably most often, it answers any number of stax-type creatures that are interfering with your plans long enough for you to win
That leaves Millstone and Reef Pirates as cards actually dedicated to milling your opponent out
The deck, essentially, tries to combine the power of land destruction shenanigans with a powerful Pioneer combo base, making it a new and exciting Modern strategy
One downside to Vehicles and Mounts is that it requires you to lose access to a creature by tapping it
That means if someone casts a ten-mana spell, they are going to be milling ten cards on their next untap step