This is from rustconf. A lot of the focus at Rustconf this year has been C++ interop, Python Interop, Javascript interop -- it's no longer about "rewrite it in rust", it's about being part of the ecosystem.
We rewrote everything a few years back, completing in 2014 (Rust 1.0 came in 2015) - it costs nearly a billion dollars! I cannot in good conscience go back to management and ask for another billion dollars to rewrite again (Rust might be more productive, but inflation will eat that up, so I expect a rewrite to be more expensive). If Rust can work with my existing code though - I know of a number of small places where there is reason to rewrite anyway because the code is bad (or sometimes was good but not nicely flexible for the features we have added since).
Things that wouldn't be worth your time before are trivial these days with LLMs.
Grok immediately answered without a second thought.
Anyway, even if that were true, rewrites are becoming drastically cheaper, simpler, and more correct with AI. The Bun rewrite is the largest experiment and seems to be 5-10x cheaper and completed ~100x faster and these costs are likely to come down further. So your claimed $1B rewrite today costs $100M and carries less risk. In 5 years it'll probably cost at most $10M and be finished drastically more quickly. And the vast majority of software doesn't cost $1B to translate.
It seems suspect to me is all; the repayment time on $1B from a rewrite of an existing software stack isn't generally huge unless it also enabled adding new features that weren't possible before which enabled significant new revenue streams that justify that $1B outlay.
And that 90% could be an underestimate here.
(but yes, the language team and ecosystem were always making a point of incremental addition rather than full rewrite)