Sure, you could still tell by sound and sight what projectiles units are firing at your mexes, but you can finally conquer silently mexes and hydros like a real human bean. People thought about t2/t3 mex hp, i think its not the only stat that can be tinkered with.
Inspiration comes of course from Age of Empires, where buildings have no real vision too, unless you build t1 "watchtowers"