> On the other hand fil-c won't help with dependencies written in C++, Fortran, and lots of others.
IIRC Fil-C is already documented to work with C++. It's not immediately obvious to me that there are any fundamental reasons Fil-C wouldn't work for Fortran and "lots of others" as well; a fairly large chunk of its work is done via a pass on LLVM IR [0] so anything that compiles to LLVM could reap Fil-C's benefits with (probably?) relatively minor alterations to frontends.
Maybe. There's rust version of libc and SSL already. On the other hand fil-c won't help with dependencies written in C++, Fortran, and lots of others.
The "less safe" gets very context dependent.