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A functional memoryview for ctypes objects would avoid having to use workarounds, such as the following:
 >>> d = ctypes.c_double()
 >>> b = (ctypes.c_char * ctypes.sizeof(d)).from_buffer(d)
 >>> b[:] = b'abcdefgh'
 >>> d.value
 8.540883223036124e+194
or using numpy.frombuffer as a bridge:
 >>> d = ctypes.c_double()
 >>> m = memoryview(numpy.frombuffer(d, 'B'))
 >>> m[:] = b'abcdefgh'
 >>> d.value
 8.540883223036124e+194
David's request that cast('B') should be made to work for all contiguous buffers seems reasonable. That said, the ctypes format strings also need fixing. Let's see what happens when "@d" is used instead of "<d":
 >>> double_stgdict = stgdict(ctypes.c_double)
 >>> double_stgdict
 dict: 
 ob_base: 
 ob_refcnt: 1
 ob_type: py_object(<class 'StgDict'>)
 ma_used: 7
 ma_keys: LP_PyDictKeysObject(0x1aa5750)
 ma_values: LP_LP_PyObject(<NULL>)
 size: 8
 align: 8
 length: 0
 ffi_type_pointer: 
 size: 8
 alignment: 8
 type: 3
 elements: <NULL>
 proto: py_object('d')
 setfunc: SETFUNC(0x7f9f9b6e3e60)
 getfunc: GETFUNC(0x7f9f9b6e3d90)
 paramfunc: PARAMFUNC(0x7f9f9b6e31d0)
 argtypes: py_object(<NULL>)
 converters: py_object(<NULL>)
 restype: py_object(<NULL>)
 checker: py_object(<NULL>)
 flags: 4096
 format: b'<d'
 ndim: 0
 shape: LP_c_long(<NULL>)
 >>> double_stgdict.format = b'@d'
 >>> d = ctypes.c_double(3.14)
 >>> m = memoryview(d)
 >>> m[()]
 3.14
 >>> m[()] = 6.28
 >>> d.value
 6.28
 >>> m = m.cast('B')
 >>> m[:] = b'abcdefgh'
 >>> d.value
 8.540883223036124e+194
This shows that changing the format string (set by PyCSimpleType_new in _ctypes.c) to use "@" makes the memoryview work normally. OTOH, the swapped type (e.g. c_double.__ctype_be__) would need to continue to use a standard little-endian ("<") or big-endian (">") format.