In all my time I've been programming in Smalltalk (since about 2000), the 
idea that Sets simply do not contain nil was a core assumption of using 
collection classes for me, not just an implementation detail. I routinely 
do "something asSet" to get rid of nils, and this change would break all 
my code.

Now, I obvioulsy do not see the value of allowing Sets to contain nil, but 
other people do. How about creating a new class to handle this? NilSet or 
whatever

rado