Recently, there was a change to speed up 
__contains__.  

x in (1, 2, 3) would be compiled as 
x in frozenset(1, 2, 3).

This was backed out, because frozensets raise a 
typeerror when asked about unhashable objects.  
These objects *can't* be in the set, but there was 
concern about supporting objects in which a mutable 
and an immutable compare equal.

So long as that is a requirement, it should be tested.  

The new test for sequences ensures that they will use 
__eq__ (and not rely on __hash__) in the future.  

The change to the rich compare tests is just a 
comment, pointing out that dicts can rely on 
__hash__ as well as __eq__.