As for how that theory will interact with reality, who knows.
At the very least, for an individual actor, it would be much more expensive to acquire 33% of all ETH than it would be to acquire 51% of the Bitcoin hashrate
The sort of software update I'm imagining is one which just zeroes the holdings of the government wallet(s), and continues the chain from just before they launched their attack.
If there's one group that the government care more about the finances of than taxpayers, it's companies. Destroying the wealth of these companies in their jurisdiction is an attack that can only be performed once, and provides no long term benefit, except for people outside their jurisdiction.
The submission you're describing requires a cryptographic proof of that validator submitting two or more existing invalid blocks that they signed. You can't just falsify that without their private keys, so what you're suggesting is not possible.
A common misconception here is that slashing happens based on what transactions you include or not. False. Slashing happens because of things such as proposing or attesting twice.