That is de facto no longer a consideration by the USPTO. Congress could force the PTO to require evidence of production. That would be neat.

In that type of case, I would expect the patent to fail the utility requirement (§101). But attacking it on written description or enablement (§112(a)) might work as well.

This is not the case at all.

If you think you've invented something, then you need to do your own research to see if what you invented hasn't already been invented. Otherwise your blinders cause you to waste your own time. That's never been new. It's the same with product names, and just about everything else (trademarks, copyrights, etc). There's even a saying for it: Why reinvent the wheel? Otherwise, absolutely everybody could claim they just didn't know it was patented, and steal anybody else's work as they wished, because "Sure I invented it after you did, but I also have a faster production line than you."

You can't claim you invented Widget-A if I already did, and can prove it. Which I would through my patent of Widget-A. If you want to invent a competing Widget-B, then invent it, and don't use Widget-A without a license with me. You didn't invent it if I already did and have a patent as proof.

That's what a patent is and what it does. It doesn't stop invention. It protects inventions from outright theft (or even accidental theft). Go ahead and invent, but if you weren't first, you aren't the inventor.