Make all software which isn't released as open source liable for the cost of security breaches?
If anything, freeware (whether open source or proprietary) should be exempt from costs. You get what you pay for, after all.
"I'll have some Beware-of-the-Leopard signs printed up."
It would increase the barrier to releasing software massively (possibly killing the startup scene altogether), but it doesn't mean software development would end.
Good.
It won't take years. We will have to train developers and create better tools. Then you will libraries and apps sandboxed, like we would not allow an IDE full access to the internet, or to the entire hard drive without permissions.
Say you get the task to build an RSS reader, you will have to choose:
1 use a language+standard library that is safe and the vendor offers some warranty
2 use an unsafe language or some unsafe libraries but you will have to take the risks and do the work to review and evaluate
3 in case you prefer open source you find a language and ecosystem where there is some foundation that even if it can't offer some warranty it accepts donations and contributions that are directly targeted on security, so you would have packages that would have a checkmark that was reviewed by a team.
So I would use a safe language(a GC one) with a trusted standard library, so now I can do the network requests to grab the XML files , parse them with the secure XML library and render the content in the safe Web View provided.
This means that the guys that give or sell me the XML library and the Web View will take the risk, but they can charge for their work. We would probably get smart developers using some extremely safe languages like math safe not Rust(safer then C safe) and this guys can write a maybe slower but 100% web view (maybe with less shiny animations).
Capitalism would be forced to invest in this safer tools and in training the developers, Microsoft ,Apple, Google will have to secure their unsafe OS and libraries but for sure it would not take 1 guy years to build an RSS reader that would not take over your data and send it to some hacker somewhere.
The fact that doctors are relatively frequently sued in the US is one of the reasons why US has very expensive healthcare. If you are rich that's fine, but almost everybody else would prefer more available (cheaper) healthcare with doctors who don't need to spend money on liability insurance.