This entire comment boils down to "we can't be held accountable because it's soooo hard you guys", which isn't even convincing to me as someone in the industry and certainly won't be to someone outside it.
A major difference between software development and engineering is that the requirements must be validated and accepted by the PE as part of the engineering process, and there are legal and cultural rails that exist to make that evaluation protected, and as part of that protection more independent--which I think everyone acknowledges is an imperfect independence, but it's a lot further along than software.
To fairly impute liability to a software professional, that software professional needs to be protected from safety-conscious but profit-harmful decisions. This points to some mixture of legislation (and international legislation at that), along with collective bargaining and unionization. Which are both fine approaches by me, but they also seem to cause a lot of agita from a lot of the same folks who want more software liability.
That's why you have three different, independent parties design everything important thrice, and compare the results. I'm serious. If you're not convinced this is necessary, just take a look at https://ghostwriteattack.com/riscvuzz.pdf.
(Your other suggestions are also necessary, and I don't think that would be sufficient.)
And you're right, I was pretty much just outlining what might be called "a good start".
When that cargo ship hit the bridge in Baltimore and people were calling for bridges to be designed to take that kind of hit, I heard a lot of "that's sooo impossible you guys" from 'real' engineers. Because it apparently is.
We can do (almost) anything, but we can't always do it for amounts people are willing to pay, where 'we' is everybody and 'willing to pay' means if you charge me what it would take to make it safe or secure, I'll redneck engineer it with none of that built in at all. People are not going to stop finding affordable ways to cross rivers or use web servers just because hard stuff is expensive.
At the end of the day, what matters is if you can, y'know, do the thing. And people just can't.
> which isn't even convincing to me as someone in the industry
Then you're confident that you can write bulletproof software? Prove it. Thankfully, as an industry we're pretty good at compromising software even if we can't write uncompromisable software.
Since we're talking about serious liability, how about put up a multi million dollar bounty for any single bug found in a non-trivial program that you write?