Regarding Realism

I don't think there's all that much of a plan. After all, the Space Stage is the furthest off. Still, my assumption is that it'll be more complex as Spore. KSP sounds like a good comparison as far as the tech editor is concerned (the previous stages' use of the tech editor is also a good baseline, but the Space Stage will make more extensive use of it).

At the same time, it would have to refrain from Dwarf Fortress and EVE Online levels of complexity. For reference, the current plans for Society Center (broad game term for towns and cities) population will have specific numbers of people with each profession (laborer, artisan, etc.), but won't go into detail about wether your individual shark-bears prefer chitin or cellulose underwear or whatever. Maybe a broad "people want x underwear, import more x."

The main fan base seems to consist of those who want Spore 2005. Granted, Thrive will be more complex, but the question is what level of complexity people want. They'd scoff at only three types of units, and shouldn't have too many problems with ten or so, but twenty is when most start to get confused, and thirty is a jawdropper.

TL;DR: Presumably balanced, depends on what folks are comfortable with when we reach that point. I think this question will be asked a lot, with the answer changing as Thrive gets more and more content to base assumptions on.