Actually that would make it a lot harder, especially due to draw distance (people with a better PC can increase this to see further), on top of that it never makes it clear for someone whether they are safe or not.
PvP players should be aware of people being in the PvP zone or not, which is easy enough to see, and PvE players should not be standing on the very edge to create confusion, if you stay a couple of blocks away, it's clear for everyone.