The C standards kind of have a main theme, eg numerics (aka eating Fortran's lunch) for C99 (_Complex, restrict, variable-length arrays, type-generic math functions, ...).
While C11 is indeed to some degree a polishing of C99, its theme is multi-threading.
Yep, I've not tried the c11 threads yet, pthreads tend to work for me and in kernel, well not like i'll be using c11 threads anyway. So its been a bit of a "maybe someday" task. :)