This isn’t a simple thing to answer as it’s specific to any given project. If something is millions of lines of code, will anyone ever fund a full rewrite that

This isn’t a simple thing to answer as it’s specific to any given project. If something is millions of lines of code, will anyone ever fund a full rewrite that could take years? In that case finding areas to plug-in Rust is probably the better strategy. See the Linux kernel and drivers being able to be in Rust. On the other hand, if something is only a few thousand lines of code, a rewrite wouldn’t take much time and might be worth it.