Presumably, any public or insider information about a credible funded technologically-sound attempt to mine the asteroid would crash the market first. So, the first sign of such an attempt would be huge shorts in the paper commodity markets by the people funding the mission. They would have to make their money on the financial hedging, not on the actual sale of mined PMs.

Perhaps it also means that Bitcoin has a more credible claim to a limited future supply than traditional PMs with a "proven 5,000 year track record".