There is a reason why modern languages use keywords like "func", "def", "fn", "var", "let" to discern between different types of declarations, for example. I dont think many languages are LL(k) (please correct me if im wrong), but C is as far away from that as it gets, for small k.
I've thought it would be nice to add func to the language. Even if it's just sugar it would help. Type inference + allowing functions to return an anonymous struct or a tuple would be super.
I started reading the C BNF and I have to admit that I was not prepared at all. It's not as easy as it sounds.
I cannot imagine how difficult it must be to maintain a modern C++ compiler.