The moment someone wants to take the economic hit of a decade+ of performance progress.

IOW, not gonna happen.

I could see coprocessors becoming more popular though. We already have AES-NI, what if the sensitive keys never ended up in CPU cache because the CPU never had to see them? Specialized HW could not have speculative execution. Granted, that doesn't prevent seeing the plain text of something that's decrypted. It's all about the threat model and what tradeoffs you're willing to make.

And that's why Intel et al haven't completely abandoned speculative execution. For the vast vast vast majority of people, the security issues they're much more likely to deal with are straight up getting scammed. Not 0 days, and especially not insane stuff like this. Unless you can turn it into a zero-click iMessage bug (or similar), meh.

I wonder at what point we will finally give up on all these "mitigations" which are otherwise pure bloat without the presence of an actual attack, and seem like they don't make things all that much harder even when there is one.

I just want my computer to go into a special "nonspeculative" mode when I open by bank's website.

PAC is a good mitigation with a good threat model: preventing ROP/JOP.

Any reason they aren't using formal verification for this kind of thing? It would seem like a very worthy investment.

We basically have zero ability to do formal verification against information leakage through cache timing attacks and the like.