I have a gaia world behind some guardians so I can test eventually, but I did notice that the +Habitability techs are giving my Laputans some habitability on normal worlds. So it's not stuck at 0, just starts at 0, so I believe Blastbeard that they have good habitability on gaia worlds. And that they keep the -60% growth rate on gaias. Maybe gaia worlds still have disease (pretty sure there's a tooltip that suggests voidborn are immunocompromised) or their bodies have adapted to zero-gravity, from a time before artificial gravity. Even a ringworld might rely on "gravity" (presumably from spin) to keep the atmosphere from escaping, while modern habitats use artificial gravity to accomodate non-voidborn on a much more compact scale.
All this breaks down if it's overthought too much, of course. Just loose headcanons to pick from.
My voidborn run had awful economic difficulties about 20-40 years in, even after conquering and enslaving my only neighbor (I started in a pocket behind a marauder clan). I'm not totally sure why, but had plenty of mineral income but was struggling for credits and commercial goods. I think I just didn't have enough pops on-habitat to get all the building slots I wanted. What fixed that was domestic servitude. The huge income of minerals and food from enslaved planets helped a lot (pseudo-thrall worlds, I really want that tech) but flooding my worlds and habitats with unemployed "servants" gave me high amenities across the board, *and* the raw population numbers to build more refineries and factories for my voidborn to work. The servants take very little housing or upkeep, and the voidborn specialists get a nice production bonus.
I currently have about twice as many slaves as voidborn, but only a few of my voidborn are mere workers. I have to keep 2-4 on each slave world to serve as rulers (including noble) and enforcers, tanking the consumer goods upkeep (I'm swimming in more food than I can use). Fortunately habitability doesn't affect happiness so these few elite basically make the whole planet "happy". It does affect growth rate, on top of the -60% from being on a planet at all, but fortunately it seems to reliably choose the slave pops to grow instead. Meanwhile it looks like I'll need to manually set population growth on my habitats to get more voidborn, as slave pops are growing there too like half the time.
Amusing quirk which was my original reason for posting: Despite having no contact with the galactic community, I got a notification when the galactic council was forming. The notification even showed me the top three empires, their names and diplomatic weight. Imagine my joy to see that my custom lithoid race is alive and well!
Project: infinite minerals is good to go~They're actually the most influential empire in the galaxy, but I'm basically tied (if not for the Isolationist stance penalty). Considering I'm currently popping out habitats almost at pace with my influence gain, AKA booming at an insane rate for 2275, I feel ready to be the midgame crisis in a few decades~
(I wonder if I can bumrush a science ship past this wall of raiders, but it wouldn't help too much. Unless I took Nihilistic Acquisition and got a fleet through to steal a lithoid pop... that would be very useful indeed. Ooh, or just bought one on the slave market if that's an option! Plus I could totally sabotage the galactic community as a council member, hehe)
So the pop growth penalty still applies? That's what I was curious about, since it looks like they actually swap traits when on a planet instead of just having a flat habitability, which in turn prevents you from just using gaia worlds or ring worlds to bypass the limitations.
My experience so far was that the game actively tries to give you bypasses for those limitations. All you really need is one migration treaty, or one conquered planet (e.g. primitives), or even nothing at all since there's an event that fires when you have pops on very low habitability planets resulting in your pops self-gene modifying.
Interesting, I wonder how that works for voidborn.
The event changes climate preference, so I wonder if the voidborn-on-planet and voidborn-off-planet traits stick around or are tied to habitat preference. I'm guessing the latter, though maybe I'll find out once I research Glandular Acclimatization for the ability to change climate preference manually.