Yeah, but would anybody want to eat an egg saturated with urea and spun on a centrifuge?
I'm not in absolute earnest here (and neither are you, I suspect). I was just geeking out. 
If you mean "the society" when you say "the world" - yes.
If you mean the true state of nature... well then that's going to be restored when the artificial state held in place by the Veil is released.
No, I meant "world." The world Solas knew has changed. He's the one who changed it, but once he gave it a push, it kept on changing. It now contains things like red lyrium and a socio-political infrastructure that shapes reality as if it were a natural phenomenon, but even if it didn't have either of those things, it would not be the same as the world he knew. As anyone who has ever worn a cast for a broken limb can tell you, things don't just spring back to normal the moment you cut the cast off.
I was actually thinking about this on my drive home. Solas tells the inquisitor a story about a spirit he encountered in the Fade who had forgotten its own identity. "I've forgotten," the spirit said, "there remains no word for what I was." Inertia is a very real thing, and Thedas seems to have its own equivalent of the second law of thermodynamics ("The entropy of a closed system always increases over time.") Ultimately, it doesn't matter whether the changes were natural or artificial, the changes were permanent.
What comes through the breaches isn't representative of the entire population of spirits/demons in the fade.
Is there a bouncer at the rifts telling spirits they aren't demonic enough to get through? Or is it simply a case of both spirits and demons getting through, but spirits becoming corrupted on contact with the corporeal world?
The Breach didn't drive them mad. Remember Cole? He predated the Breach. He entered the world to help, but what did he do? He killed a bunch of mages. He meant well, but that doesn't make those mages any more alive. He didn't understand the world. He was confused. He knew he was killing people, but he thought he was helping.
Cole is a spirit of compassion, and his intentions were completely above reproach. How will more ambiguous spirits react? We've already had a brush with Justice's failure to adapt, and I don't imagine Valor or Zeal would do much better. If the Veil is no more, there will be nothing to prevent spirits of every description from dropping into the world, and there won't be a patient guide to help them adjust. Spirits don't adapt to changes very well, Solas tells us. He says they don't grow, that they don't understand emotions, they embody them. Plus, the natural state for a spirit is what Solas describes as "a peaceful semi-existence." Change to their environment is likely to be damaging.
To summarize, however well or poorly both ancient and modern races might fare in a merged world, spirits will probably fare far, far worse.
In the end, which would weigh heavier on Solas's conscience? The knowledge that he was responsible for the destruction of the elvhen or the knowledge that he was responsible for the destruction of the elvhen, modern peoples, and spiritkind? Then he really will die alone.