Just out of curiosity, what are the use cases for assertSameElements? If one has two objects, doesn't care about the order and the duplicates then these two objects are most likely sets and assertSetEqual can be used instead.
OTOH checking if two sequences have the same elements regardless of their order seems more common, and I don't see any method that does it (I was expecting assertSameElements to do that).

I would be -0 to add another method -- the API is already too confusing IMHO (is not so easy to remember if it's assertSameList, assertSameLists, assertListEqual, assertListsEqual; also note the 'assertItemsEqual' in msg98697, 'assertItemEquals' in msg98717).
Maybe a check_order arg in assertSequenceEqual (or was it assertSameSequence? ;) would be better, or at least more explicit.