I have no doubt this proposal or any other similar proposal would work well in the 90s or early 2000s. Let's go one step further and let browsers work with all those third party website and figure all the details for sharing, and websites never embed anything.
But you see, that's not the problem. These share buttons are often trojans on websites. Facebook tracks you via those share buttons even if you have never had a Facebook account. And people come up with various solutions to tackle that -- adblockers just block network traffic, while a small amount of website owners create a separate switch which you can toggle and then share with Facebook. Isn't all of that stupid? I don't see why Facebook, Instagram will be eager to opt in to this solution and make the experience good.