I feel you are overly optimistic.
If we want to do this kind of lockdown, we'd need some way to make computers only run authorized software. We'd need a standard for digitally signing OSs, and the BIOS would need to check the signature and enforce that only signed OSs can run. Then the OSs would need to run only whitelisted software.
How hard would it be for governments to coordinate getting a lockdown feature like that into every computer? Well... they don't need to. We already have it. MS has already bludgeoned everybody into supporting Secure Boot, which is exactly this feature/misfeature, in all new computers that ship with Windows (which is most of them -- and the rest support it too because nobody's going to make a separate motherboard just for computers that ship with Windows).
Sure, you can disable Secure Boot... except for when you can't. There are machines (often, not always, laptops) out there right now which don't let you disable Secure Boot, so you're stuck running only approved OSs on them. (MS do the approving, in case you were wondering.) It wouldn't take much at all to expand that to every machine; all it'd take would be MS adding "in order to keep machines secure, don't allow disabling Secure Boot" to the Windows Hardware Certification requirements
Given that we already have systems that will only run approved OSs, it doesn't seem like such a huge leap to "you can only run the software we let you run", especially when all the technology to make that happen is already in place. And, for that matter, being used routinely on tablets and phones.
The coming war on general-purpose computing and The Coming Civil War over General Purpose Computing are a good idea to read. I really wish I had my tinfoil hat on here, but sadly this is looking all too realistic.