Well Exos seem to be walking metal skeletons and are quite humanoid in appearance compared to the bulkier industrial designs you'll find in comic books and animes. One of their sources in development of this race was Appleseed an anime that featured a similar note in a great city on a vast frontier of war and desolation with many types of humanoid life walking around. One of those races were massive living cyborgs that we're crafted in various shapes and sizes. It's not too late Bungie to add some extreme Exo designs to their customization. Many PVP players will want lithe hard targets and that's fine. But you have now another grouping out there that enjoys PVE and RPG elements in FPS's and so interesting designs and sizes appeal to these players. Trust in your player base they will known to switch out between character hit box sizes or they'll learn quickly enough to do so in PVP matches. But for them being some massive alien armored Exo standing on a Martian landscape with wind whipping around them taking on the Cabal is just as appealing as stepping into a PVP match to gain a visible ranking. You're appealing to RPG players from Skyrim and Dragonage, Monster Hunters, Final Fantasy, and Dark Souls with Destiny as well as your Halo fans. Just like Halo fans they have specific tones in gaming they are looking for in long term player investment.