There's many differences between both implementations.
I don't know if we can live with them or not.

~ $ ./python 
Python 3.1.1+ (release31-maint:76650, Dec  3 2009, 17:14:50) 
[GCC 4.3.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from xml.etree import ElementTree as ET, cElementTree as cET
>>> from io import StringIO
>>> SAMPLE = '<root/>'
>>> IO_SAMPLE = StringIO(SAMPLE)


With ElementTree

>>> elt = ET.XML(SAMPLE)
>>> elt.getiterator()
[<Element root at 15cb920>]
>>> elt.findall('')  # or '.'
[<Element root at 15cb920>]
>>> elt.findall('./')
[<Element root at 15cb920>]
>>> elt.items()
dict_items([])
>>> elt.keys()
dict_keys([])
>>> elt[:]
[]
>>> IO_SAMPLE.seek(0)
>>> next(ET.iterparse(IO_SAMPLE))
('end', <Element root at 15d60d0>)
>>> IO_SAMPLE.seek(0)
>>> list(ET.iterparse(IO_SAMPLE))
[('end', <Element root at 15583e0>)]


With cElementTree

>>> elt_c = cET.XML(SAMPLE)
>>> elt_c.getiterator()
<generator object getiterator at 0x15baae0>
>>> elt_c.findall('')
[]
>>> elt_c.findall('./')
[<Element 'root' at 0x15cf3a0>]
>>> elt_c.items()
[]
>>> elt_c.keys()
[]
>>> elt_c[:]
Traceback (most recent call last):
TypeError: sequence index must be integer, not 'slice'
>>> IO_SAMPLE.seek(0)
>>> next(cET.iterparse(IO_SAMPLE))
Traceback (most recent call last):
TypeError: iterparse object is not an iterator
>>> IO_SAMPLE.seek(0)
>>> list(cET.iterparse(IO_SAMPLE))
[(b'end', <Element 'root' at 0x15cf940>)]