VoIP is usually hard as hell to implement. I remember the WarZ devs working their asses off just to get something slightly working, and then work even further to make it stop fucking everything up.
Not sure I've ever heard of WarZ devs working their asses off. Not sure I can even imagine it
But yea VOIP would be nice but its a huge undertaking which might not be possible with the Unity engine tbh
Edited:
I'd prefer a more advanced chatbox, easier to read (because you need a fucking microscope to read it right now) and with both local/global chat.
Local chat would be great. Something like a 100/200 meter range or something