Platform for people to publicly make/check predictions about the future?

Yes/No Predictions. Example: Will X have happened by date Z, yes or no?

People can submit a prediction. Their predictions will be kept encrypted until date Z has come and then it can only be decrypted by them.

If they want their answer (linked to their account) to be publicly visible, they can choose to decrypt it for everyone to see what they predicted.

Yeah, sure everyone can do this on their own blog or social platform by publishing a hash of the prediction and then later showing their answer.

But a platform/tool would be handy.