I think that's technically possible, but you have to use a freshly allocated (and zeroed) buffer every single time, since after it's been written to once, it's 'tainted' with the effective types of the structs stored in it. (Though it looks like the ISO C2y draft finally has language to address this case, with a concept of "byte arrays" that can hold objects of other types, as long as you keep alignments in mind.)

The bigger issue with ISO C and POSIX is everything around 'struct sockaddr': you don't have any way of knowing what types the implementation is internally reading in or writing out. If you give it a casted pointer to a 'struct sockaddr_in' but it reads the sa_family from the 'struct sockaddr *', that's UB; ditto if listen() gives you a 'struct sockaddr_in' and you read the sa_family from a 'struct sockaddr *'. Or if you use 'struct sockaddr_storage' at all, that's also UB. IIRC, the latest POSIX edition just tells implementations to "pretty please allow aliasing between these types in particular!"

Of course, POSIX has nothing on Windows APIs, many of which encourage the caller to cast around pointers with impunity. As far as I'm aware, MSVC doesn't care about strict aliasing at all, and only has a minimal set of optimizations for 'restrict' pointers.