In unittest, DictContainsSubset() should be removed from 3.3.  It was defective by design (wrong argument order).  I concur with Ezio that the other unittest methods should remain intact.  I'm not sure whether assertSameElements() should stay or go (when Google's code search was still up, it showed zero uptake for that test method, so it may be better to remove it now).

The Decimal module's Context._clamp should also be removed from 3.3.  It was a private API from the outset and won't be mirrored in the C version.  It looks like Mark has already done this one.

I also agree Antoine that most of the other changes shouldn't be made in 3.3 except for the three he listed: max_buffer_size, get_prefix/set_prefix, and the argparse deprecations.