I saw Satoshi drinking a pina colada at Trader Vic's. His hair was perfect.

Note carefully: this is not about declaring previous behavior to be retroactively legal, it is about passing a new law that would wipe out current lawsuits. This is different, and it has been done many times in the past. (After 9/11 a new law was passed to prevent thousands of expected lawsuits from being filed by victims' families.) This approach can serve a useful social purpose if used approriately, and the question is whether the tactic is appropriate to protect heavily-regulated companies who may have "over-cooperated" with government.

BTW it's good that you know the constitution because the 'ex post facto' thing is emphatically not dead, which probably led to the end run described in the article.