I was scouring the WZ Fan Kit one day (as you do) and I noticed that the sound files had some interesting files we hadn't seen before in game. I didn't have a look at all of them, and I don't remember all of them, but I'll list a few here.
Flamethrower_poison "You've got an infestation" "Call poison control immediately"
Medic_nurse "I'm not the squeamish type" "Lets check your vitals"
Sniper_mortar "Shock and awesome" "Calculating the distance"
Brawler_generic "Let's go!" "Bring it on"
Brute_generic "H-h-here I come!" "Hey! Friends!"
Infector_puppetmaster "I pull the strings" "The man, behind the curtain" for some reason there seems to also be a 'child' version of these quotes too, in a sort of announcer voice
Spitter_anti-air "Something in the air" "Aim high!"
Spitter_chainlightning "I'm very catchy" "What goes around, cackle"
Squidfinger_hippie "Welcome to the jungle"
All of the units I've stated above all have 2 spawn, attack and death lines. I didn't have time to listen to all of them, but they're there. Speaking of, most of the currently existing units have certain sound files that aren't used. For example, all units have 1 spawn, attack and death line. But the sound files have 1 more of each. Whether these were auditions, didn't make the final cut, or appear in game, just plain rare, I wouldn't know.
What we can gather from the unrealeased/in development units:
-There was going to be a poison element
-There were going to be air units
-There were generic versions of units
-The survivors had an explosive unit (though we had already seen the mortar before, so not big surprise)
I'm sure I missed a few, so feel free to check the WZ Fan Kit out for yourself.