Sounds like you are describing Zig. https://ziglang.org
> > using the new language's compiler as the project compiler front end's drop-in replacement (without having to make any changes to the code at all for this first step)
I'll look into Zig more, though. Maybe I'll like it.
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I stand corrected, given my phrasing. I should have specified that it needs to also support incrementally adding the new language's features while most of the code is still unaltered C, rather than (for instance) having to suddenly replace all the includes and function prototypes just because you want to add (in the case of Zig) an error "catch" clause.
This might come with huge drawbacks, but it still seems like the only socially acceptable way to fully replace C at this time; make it so you can replace it one line of code at a time in existing projects.