The split buffer data structure commonly used in text 
editors to efficiently manipulate text and data attached 
to that text can be implemented using the Python array 
type with the addition of a way to rapidly copy data 
within arrays. There may be other situations in which 
rapidly copying blocks within an array is useful.

-- Neil Hodgson

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Moving to feature requests.

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How does this differ from slice semantics?

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If you are asking how the copyrange differs from a sliced
copy like
>>> import array
>>> a = array.array("c", "0123456789")
>>> a
array('c', '0123456789')
>>> a[5:8] = a[0:3]
>>> a
array('c', '0123401289')

   There is an extra object creation and copy for the
temporary slice. I think the actual copy between slices of
the same type is fast. Possibly the original patch was lost
so it can be found at
http://scintilla.sourceforge.net/arraycopyrange.diff
   I didn't chase this much before as it may be better for
me to produce a 'text' class that combines more features
into an efficient mutable document type.

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The 'text' class is likely the way to go.

I see your point about the extra object creation.  However,
given that there is currently a way (not a good) to do it,
does the use case warrant the addition of non general
purpose method.  I don't think so; even lists don't have
copyrange().

Am closing this request.  If you change your mind and decide
that this is an essential addition, feel free to re-open it.