I think we are talking about 2 different things. The retrospective law was passed
after an existing case was decided in favour of Vodafone. People may not be worried about incarceration, but they could still be concerned about excessive taxes. Excessive taxes (imposed retrospectively) would effectively result in the government seizing your bitcoins (as taxes).
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Taxation implication in terms of retrospective effect should not happen as retrospective amendment in itself means an amendment in existing provision. I am not suggesting that an retrospective tax implication cannot happen but surely there is a remote probability that it will happen.