[reirob]

There is actually a similar question that is asked in the interview:

> Is there anything in the kernel which is not optimal, but would require a complete rewrite to address properly? In other words, the kernel is 30 years old and knowledge, languages and hardware have changed a lot in these 30 years: if you rewrote it from scratch now, what would you change?

And Linus' answer was very interesting for me - and after reading it, I would answer your question (tongue in cheek): "Never, because it seems that Linux developers were quite successful in starting all over again for quite some parts of the Linux kernel."

I guess it's not really an answer to your question, but kind-of ;)

[kingsuper20]

No doubt any replacement would have to be enough better that it's worth the cost (opportunity and otherwise) to both produce and switch to it. Perhaps security/privacy issues might drive a serious rehatching of commonly used software.

It occurred to me that there's enough inertia at this point that you'll likely only see ground-up architecture and/or implementation when some sort of hardware substrate is produced that requires it. Until then, we are on the karmic wheel of cpus that drive os/language design that drive cpu design.

[sagarm]

Google is building a new OS called Fuchsia, with no new hardware to drive it was far as I know.