It's long been conventional wisdom that you shouldn't write your own crypto libraries - leave that to experts. But excellent open source libraries are available, which do get reviewed by experts. And if you're willing to study, maybe you can learn enough about cryptography to become one of the experts?

I'm wondering what other security-sensitive software that might become true of in the era of Mythos-or-better AI's?

There will still be open source projects that anyone could learn enough to contribute to, but maybe starting from scratch and writing your own becomes less feasible if you aren't attracting enough attention to get attention from people with access to the best AI's?

For example, Linux patches are going to get expert reviews, but maybe your homegrown OS won't?