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Starting with the example in memoryview documentation:
>>> from ctypes import BigEndianStructure, c_long
>>> class BEPoint(BigEndianStructure):
... _fields_ = [("x", c_long), ("y", c_long)]
...
>>> point = BEPoint(100, 200)
>>> a = memoryview(point)
I am trying to unpack the resulting view:
>>> a.tolist()
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
NotImplementedError: memoryview: unsupported format T{>l:x:>l:y:}
>>> struct.unpack_from(a.format,a)
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
struct.error: bad char in struct format
>>> struct.unpack_from('>ll',a)
(0, 100)
It looks like there is one or more bugs in play here.

It's deliberately not implemented (and documented): Since memoryview is a 
complete rewrite, I tried go easy on new features in order to facilitate
review.
My plan was to implement struct packing/unpacking in 3.3.1 in the same
manner as in the new equality function.
The struct error you see is tracked in #3132.

What about
>>> struct.unpack_from('>ll',a)
(0, 100)
shouldn't that return (100, 200)?

'>' in struct syntax implies "standard size" for 'l', which is 4 bytes.
ctypes uses machine size for c_long, so on an LP64 machine you can unpack 
the data as:
>>> struct.unpack_from('>qq', a)
(100, 200)

Closing, since the main request is tracked in #3132.