[spoiler=massive monologue about various races and applying science to them]
I have been working on a story that works on a similar premise and I see room for overlap so…
Basically I am building how universe not like our own might work and building laws around them and stuff and it breaks down like this.
There are Three Universal “foci” that universes function on, some only function on one, other use two or three to various degrees. The “foci” are Natural, Magical, and Technological (like Earth).
“Natural” based realities/physics being like Starwars “The Force” and general Gaia type worlds/natural laws Creatures having heightened sensitivity to the world around them and good “sixth sense” seeing auras, and telepathy and such generally fall into this reality. Most natural based worlds have a big focus on unity/hivemind and or balance of living and/or nonliving things.
While
“Magical” : based realities/ohysics being very Eragon or “The Name of the Wind” transfer of energy. Every “spell” and manipulation having a cost however finite it may be. Pulling the heat/light/motion/chemical/mass energy out of an object or being and using that to power a spell that creates or changes energy. Making/ increasing heat, light, fire, chemical and/or mass energy. Note that alchemy would fall under the magical umbrella.
and of coarse “Technological” realities are very orientated around the magnetic and electric properties that form them from the highly reactive nature of electrons in “Tech” universes.
Tech based races focus on the use the increased reactivity of electrons to create both high reactive explosives, nuclear weapons/energy, as well as highly UN-reactive stable multi-bonds between atoms to create alloys and strong material.
So for Cata purposes… you could…
The other “Nature” and “Magical” Races are from other dimensions and the focus of the DDA Universe has been thrown into flux making the ‘return’ of the races practical as they rely less on technology than we humans do, preferring more nature and magic based realities where they can be more comfortable and ultimately stronger (like a fish in water as opposed to out) Due to the new flux they have all begun exploring, trading, and some even establishing forward bases, and outposts on the ‘renewed’ Earth ‘Frontier’
Not so much “they went into hiding” as our world simply became an impractical place for them to be as our world shifted into a “realm” of technology, and so they left or waned in ability until the “natural” and “magical” physics returned.
Then mix and match realities/universal properties based on what the race demands. So Kobolds, probably mostly natural with some magical as well. Elves? Very high in Natural and Magical, not much tech. The locations they come from follow the same rules/outlines. Makes for a universe multiverse that can quickly be grown to epic proportions with very little effort. I look forward to having my characters run through an odyssey rivaling homer, using the laws/ physics I have laid out.
First place main character visits is Technological planet that has lost all technology in a matter of months due to a universal focus shift in their realm and is now a planet filled with overgrown ruins from a society that tore itself apart when the Technological laws that were holding up their world fell out from under them.[/spoiler]