Won't work. Malicious actors (both malware developers and companies with user-hostile business models) will start working around it, by for instance giving you two applications, one connected to the Internet and one not. The first application will be the C&C server, the second one will be the executor, and they'll talk with each other over e.g. files in first application's folder.
Trying to block that would pretty much hose all utility in having a general-purpose computer. You'll be back to the crappy UX of a smartphone.
I honestly don't know how to solve this conundrum. You can't solve it technologically, as you quickly hit the Halting Problem. You can't solve it socially, because for any power user benefiting from the modicum of interoperability you leave in, you get 10 regular people who can be trivially social-engineered into selfpwning their device. It seems that in the end, you'll either have to lock down computers to near uselessness, or live with the risk of bad actors exploiting them.
Ideally users would be wary of what they do with their computers, but considering how the world devolved from "you should never use your real name and address online" to modern social media, this is yet another case where i do not see such an ideal happening.
This is exactly the type of problem it solves, usability with security.