1) Getting readers to consent. Oh, sure, they might unknowingly "consent" if it's buried in the TOS. They might even explicitly consent if you present them with a one-time consent form that implies it's making use of resources that would otherwise be idle. But then their laptop starts to heat up every time they visit the site. If they leave the tab open, other apps appear sluggish. Eventually, they're going to notice that they're not actually giving away something that has no cost to them. It's more like loaning someone your car when it would otherwise sit parked in your driveway. Eventually you're going to notice wear on your car, and an empty gas tank.
2) Digital advertising revenue is insufficient, by a significant margin, to replace print-ad revenue. I would expect the revenue from this type of arrangement to be low enough that it doesn't solve the problem, but only stems the tide a bit. Perhaps some publishers would be willing to invest the time to integrate with this, even if it's a comparatively low revenue stream. But I think most publishers are investing most of their energy looking for the true game changer: a business model that can actually sustain their business.