Sebastian:  I think this discussion is a bit off-topic for this particular bug;  you might want to raise it on python-dev or python-ideas instead.  

Bear in mind, though, that the behaviour of NaNs and containers has been discussed to death many times in the past;  I'd suggest not bringing the issue up again unless there's something genuinely new to bring to the discussion.  The current behaviour is certainly a compromise, but it seems to be the best compromise available.

Note that with respect to this particular issue: it's only *signalling* nans that raise on hashing for the Decimal type.  Quiet nans are hashable as usual.  Since for float, all nans can be regarded as quiet, Decimal and float behave the same way on this.