Cheers, I'm not looking to implement these concepts for long while yet, but I have fun thinking of them.
Here is some minor progress...
For the matriarch I was thinking of giving her a hood an "acid-shotgun" spit, and I was redesigning the look of the snakemen to be more alien looking. The newts are still not looking right in my mind. I went for a cthulian vibe on the ethereals.
A unit I've been thinking of is a Goo type enemy that starts as a tftd CALCINITE and on death spawns goo that "kills itself" to infect a soldier that becomes a zombie that when dead spawns the same goo, and so on. The idea being the goo needs a host to survive. The goo would be weak to fire but highly resilient to conventional damage.
And to keep the variety going the chryssalid would no longer spawn zombies, rather the unit it "kills" would remain fully in control of their own actions until they birth a chryssalid-nymph. This'd make infected civilians harder to spot and allow infected troops to go out in a blaze of glory.
These are still just ideas atm though.