Well, Clarion (White Light) is supposed to be undergoing a terraforming process. Large parts of Kraatar (Tristkar), Volturnus (Zebulon), Laco (Dixon's Star) and a few others aren't exactly shortsleeve planets, but TSR gave us a bunch of M-Class (oops, sorry, a bit of Star Trek speak there)... ahem, garden planets to play on in the Frontier.

I have one of the S'sessu worlds with a slightly toxic atmosphere and the worms want to terraform that. Maybe some of the Vrusk worlds which we have very little information on need to be terraformed... or vrusk-aformed... insect-aformed?

The Outer Reach doesn't sound like a shortsleeve environment either.

But since GOD Co. is supposed to exist in the game -- thanks to Zebs -- where is it supposed to be operating? 

This brings up the idea of Terraforming as a weapon, which appears in sci-fi literature and TV shows as the plot more than a few times. Sometimes the Terraforming species has no clue they are destroying sentient life so accidental, sometimes they get their and oopsy a civilization but oh well just a bunch of primitives who cares or it is just a single organism who cares, sometimes they always knew about the other life forms and it is all part of the plan to make the universe a better place by destroying those life forms, or they terraformed a planet a while back in complicated 1000's of year science project and colonists of another species land and muck up the terraforming plan and when the original terraformers show up instant conflict and so on. It is only logical that UPF races might be part of such plot lines. Terraforming technology encountered need not be UPF race tech and could be more advanced or less, on auto pilot or manned. Let's face it an automated Terraforming mega-ship that is armed with high tech weapons and defenses homing in on a colony could ruin anyone's day even the Sathar, not to mention being a prize worth fighting over, but so would a bunch of terraforming "asteroids" being hurled from deep space homing in on planet the Core 4 or Sathar happen to have a bio-dome operation on. 

Dr. Who had plot where the Doctor and friend stumble into a war between to factions one human, one fish people fighting a war of cloned generations underground the planet, and everyone wanted the source... turns out the cloned people who where on some ridiculous number of generations on both sides, with a garbled memory except how to kill well had only been on the planet less than a month I think it was maybe 1 week. (Pretty deadly war) And the source was the means to start the Terraforming and end the war, as plots go it could be adapted to SF with some changes of course.

I always figured there is a wide range of habitat possibilities for the UPF races and the Sathar. There could be underwater cities, moon bases, bases on inhospitable hazardous planets all requiring specialized habitats and technology suited to the colonizing race or races.  

I think the worlds being adapted to the UPF races tend to require less work in the material so it seems a more primitive Terraforming is being used instead of say completely destroying all life to create new life processes or it could be the UPF approach is about cost effectiveness and expediency. If "garden" or near garden planets are around a lot in a setting it might be cheaper and easier to colonize those and tweak them, versus say Green a planet like Mars. On the other hand if Garden planets are rare then that makes them prime real estate to fight over and gives a boost to the desire to terraform planets that would need a lot of work. Also you have to ask why, why terraform or why not terraform, why is the race in place X in the first place? Is there a profit to be made, a military or intelligence gathering reason to be in place X, is a rock in the middle of nowhere disputed territory, secret base of someone's, rare resource location that makes it profitable... and when the place is no longer profitable, no longer disputed territory, no longer habitable for some reason, no longer secret or of tactical value, the rare resource is no longer used by the society, what happens then and how many abandoned such places could be out there?

On the no longer habitable aspect, what if a planet is not habitable to it's original occupants but by some accident of fate is now habitable for the Core 4... what would that look like to the Core 4? How would that happen? And would the original owners be okay with new tenants sulking around their old world?

Interesting what might happen if a scientist discovered a microbe or spore on an ancient yazirian artifact that was not in the genetic catalog of the Ark. Fo1 will alledged it's modern contamination or recent mutation, they'll censure the scientist attempting to trash his reputation, destroy his findings and make the evidence disappear- Raiders of the Lost Ark style disappearance of the artifact. They'll loudly proclaiming their version of the facts. 

Hhhmmmm potential there for a Triad Institute of Technology team adventure. 

I am considering the idea of Pavor having 2 inhabited planets, one being Waloo and the other Yazira, thus both worlds had to be abandoned. This might also help explain the advanced terraforming ability of the Yazirians. 

Yaziria is also an Eden Like idea in the literature as well.

From a psychological-sociological perspective the loss of one's land is a big deal so the lost land becoming a paradise lost, a place envisioned as better than it probably was makes sense. So it ceases reflecting the reality of Yaziria and becomes the ideal as reshaped by fond memories and religious leaders.

Just my thoughts on the names.