> Then again, nearly none of the syntactic C features post-C89 have been very compelling or widely adopted.

That's Microsoft's fault; it's 2020 already, and unless things changed since I last looked, their compiler still doesn't have full support for the C99 standard.

Even then, some of the C99 syntactic features have been somewhat widely adopted (at least when not compiling for Windows); off the top of my head, we have "//" comments, declarations in the middle of a block, and designated initializers.