The SMAC Transcendence victory is a combined technological/wonder victory. You complete a device that uploads humanity's collective knowledge to the planet's mind (thus freeing it from the cycle of dying as it reaches sentience), then upload every human consciousness that is part of your faction.
Ah, gotcha. Makes sense!
It's not particularly similar since Planet in SMAC is a juvenile entity while Ivoria's intelligence (is it still called Ivoria?) is firmly in control.
Not Ivoria. It was called that for the briefest of times, heh. The actual name is "unknown" unless you do one of the special victory conditions that pits you directly against the planet, during which you'll have direct discussions with it where most of the important secrets get revealed the closer you get to victory.
Speaking of story stuff though, how early in the AI War did the AI blow up Earth? Just met IMT and was curious.
I don't have real specific timelines for that, mainly because there didn't need to be yet and someday there _might_ need to be a reason.
To expand on Watashiwa's answer, the Transcendence victory in SMAC is the top of SMAC's tech tree. The total contents of the in-universe Internet gets uploaded to the planetary consciousness, successfully bringing said consciousness into full-blown sentience. You then instantly get access to a project that allows you to make your own consciousness an integral part of the planetmind. Of course, every other surviving faction in the game gets the same opportunity, and only one of you actually makes it.
It doesn't sound like the Thoraxians play exactly the same role as the Alpha Centauri planetmind, though. Unless, of course, you've got the planetmind acting in place of the normal Hive Queen... 
Ah, very cool. And nope, the Thoraxians and the SMAC planetmind are very very different. The queen is more like a lieutenant of the planetmind. Or the leader of its main army, if you prefer. But not its only army.
If you're doing something that is very likely to piss off the planet a lot, you can concentrate that in a smaller city that is very heavily defended and that doesn't have your key other buildings in it, and then have the planet really bang on that smaller city while leaving your main one more alone.
In that case, I'd actually want it to be my big city (as it stands). Energy generation and population are the major causes of planetary rage, they dwarf everything else. This means that my main city is already creating an enormous amount of rage, on top of that another 100-500 points isn't going to make much of a difference.
And that's precisely why balance isn't finished yet.
Things need to make you incentivized the right direction. Or, to put it another way, make all directions valid-but-different.
That said, one thing to recall (if you have noticed) is that planet rage is localized to each city. So if you can direct the ire of the planet away from your main population center, then ultimately that's a very good thing for you stability-wise. Right now there's not really a mechanism for doing that properly, which needs to change. I'll be doing some noodling on that.
Aha! THAT is something you will find out once I have the actual voiceovers and whatnot in place for those special victory paths. During your progression towards those victories, you start finding out some lore about this game, and the universe that it shares with AI War and TLF. My lips are sealed. 
three cheers for sweet delicious consciousness destroying lore!. ps had a nutty idea a couple of days ago regarding the snake men(I'm just going to call them that from now on since I am incapable of remembering their name) witch ill make a topic for before I send it to mantis
Cool stuff, thanks! (And it's Yali).
