Shadowrun/WMG

The Matrix is a metaplane
It would explain why it seems to act like the idea of Cyberspace as a place you go to visit.
 * And why so many of the authors had a hard time remember that decking does not equal Astral Projection...
 * Jossed: Matrix work is affected neither by magical barriers or astral background count. Likewise, magic is not affected by Faraday cages or lack of Signal/high Noise.

Spirits are responsible for Meta-Humanity and changelings
After the awakening of magic humanity subconsciously conjured spirits with the ability to possess people, the thing is that the spirits are limited to Metamorphosis and/or Baleful Polymorph

Edge is coded into standard humanity's 'Junk DNA'
Before the Awakening, metahumans were standard humans, with their metatypes traits in their junk DNA. But, what is in the junk DNA of baseline humans; it's not metahuman traits, after all. Well, what attribute do humans have different from the other metatypes? Edge. Humans have lucky genes.

Earthdawn is set in the Nth age
An alternative theroy goes that Shadowrun occurs BEFORE Earthdawn unknown to the people of Earthdawn it's now the year 5000 and the past 2000 years have been "things" coming through, kicking the planet and people over until it has managed to return to the state it's found in Earthdawn.
 * Jossed by the tie-in novels, which explicitly have Earthdawn canon events occurring in the past history of Shadowrun-era immortals.
 * Also Jossed by Word of God that Dunkelzahn (of Shadowrun) is the same dragon as Mountainshadow (of Earthdawn), and since the Big D's kinda dead now that means Earthdawn has to be the past.