Zero-sized arrays are not standard. Accessing an array out of bounds is UB. At the very least, you should use a flexible array member instead (char payload[];).
But even if you did that, strict aliasing implies that 'payload' can only be accessed as an array of character type. It is correct to memcpy between 'payload' and another object of arbitrary type T of the appropriate size (as list_push_ does in your example), but it is UB to access 'payload' in place as a T (as main does, by casting to struct point * and dereferencing). Oh, and 'payload' may not satisfy the alignment requirement of T.
There is no realistic strict-aliasing-abiding way around a distinct node type per payload type.
But even if you did that, strict aliasing implies that 'payload' can only be accessed as an array of character type. It is correct to memcpy between 'payload' and another object of arbitrary type T of the appropriate size (as list_push_ does in your example), but it is UB to access 'payload' in place as a T (as main does, by casting to struct point * and dereferencing). Oh, and 'payload' may not satisfy the alignment requirement of T.
There is no realistic strict-aliasing-abiding way around a distinct node type per payload type.