> The list of supported software is astounding: CPython, SQLite, OpenSSH, ICU, CMake, Perl5, and Bash, for example. There are a lot of things in that list that nobody is likely to ever rewrite in Rust.

Interestingly, I agree with your point in general that there's a lot of software that Fil-C might be a good fit for, but I hesitate to say that about any of the examples you listed:

* CPython and Perl5 are the runtimes for notoriously slow GCed languages, and adding the overhead of a second GC seems...inelegant at best, and likely to slow things down a fair bit more.

* Some of them do have reimplementations or viable alternatives in Rust (or Go or the like) underway, like Turso for SQLite.

* More generally, I'd call these foundational, widely-used, actively maintained pieces of software, so it seems plausible to me that they will decide to RiiR.

I think the best fit may be for stuff that's less actively maintained and less performance-critical. There's 50 years of C programs that people still dig out of the attic sometime but aren't putting that much investment into and are running on hardware vastly more powerful than these programs were written for.

Yeah, for that reason perhaps Perl5 is a better example than CPython, but something less widely used might be a better example. tcsh, say.