"C essentialist" is a line very hard to hold, because C via ISO is moved towards an horrible language like c++ (generic,__thread,etc). So, it is not C anymore, it is simple and lean C which should be the target of an essentialist line of conduct.
Whatever, a good new language would first and above all be easier to write a compiler for than simple C.
To access TLS-ized system variables (for instance errno if I really need to, I would use the sysv ABI __tls_get_addr() function).
But in the application domain, I would use pthread TLS.
