That brings up a good point. Remember what new ability the Ghosts have:

"Turning the canister rifle into a one-shot kill on any biological unit."

All Zerg are biological. That's one hell of a disadvantage. You can just see a Ghost playing pop goes the weasel with an Ultralisk's head. That's one scary ability if you're big into the Zerg. A half-dozen Ghosts annihilating a swarm of hydralisks or Lurkers is one thing, but if you've got a dozen Ultralisks all getting sniped from nowhere, that sucks.

I wonder if the Zerg will have an armor upgrade to prevent that ability from penetrating and making the kill.

The new Terran units are given a backstory of being produced to cover the shortcomings of the previous units. The air/land transition of the Vulcans, etc. The Protoss ones are coming from the Dark and Light Protoss reuniting, and in the case of the Colossus, the Protoss digging up the past weapons of war that were "sealed."

I wonder if the Zerg upgrades will have to do with Kerrigan's past. She was a very powerful psychic as Ghosts go, which was related in one of her early missions. Protoss cloak, Terrans cloak, Zerg had burrow, but I wouldn't be totally surprised if a few Zerg units cloak too.

One thing we have seen are the Nydus Worms. In that early demo, Zerg could come out of anywhere now, no creep required. Run a zergling up, burrow. Build a huge force and suddenly 4 Nydus Worms burst out in the middle of the enemy base. That's pretty disconcerting.

I'm not going to make any specific guesses, aside from the armor upgrade preventing instant death, but I could see the zerg have a few general upgrades.

- Aforementioned armor upgrade (higher level)
- Incorporating the new terrain height ignoring units, the Zerg could have several units doing it. Something like "Spiny limbs".
- Many new air units. Offensive Zerg Air has always been a little weak. Guardians too slow, Scourge good for defense, but not against anything on the ground, etc. Maybe Scourge can turn into bombs for ground units only. It seems to be a trend.
- A lot of building upgrades. The Protoss have mobile photon-cannons, and phase prisms, the Terrans have the planetary turret and retractable supply depots, the Zerg could have something equally revolutionary, like a very cheap larvae-producer (for faster swarm build-ups) or something equally huge.