Obvious kinds of humans include:
Dead humans. (Who didn't manage to leave the coins to their heirs.)
Cryonically preserved humans hoping to use them later. (Including an obvious specific candidate.)
Humans optimistic enough about Bitcoin to think current prices are too low. (We know Nakamoto had resources, so it seems a safe bet that they could keep living on ordinary means for now.)
And the obvious: you don't know that all of Nakamoto's coins fit the standard assumed profile. It's entirely possible they intentionally mined some with the regular setup and are spending a few from that pool.
The advanced answer to this is to create conditional prediction markets. For example: a market for whether or not the Bank of Japan implements a policy, a market for the future GDP or inflation rate of Japan (or whatever your preferred metric is), and a conditional market for (GDP given policy) and (GDP given no policy).
Then people can make conditional bets as desired, and you can report your track record, and so on. Without a prediction market you can't, in general, solve the problem of "how good is this prediction track record really" except by looking at it in detail and making judgment calls.
I hope you have renter's insurance, knowledge of a couple evacuation routes, and backups for any important data and papers and such.
I'm not aware of any legal implications in the US. US gambling laws basically only apply when there is a "house" taking a cut or betting to their own advantage or similar. Bets between friends where someone wins the whole stake are permitted.
As for the shady implications... spend more time hanging out with aspiring rationalists and their ilk?
The richer structure you seek for those two coins is your distribution over their probabilities. They're both 50% likely to come up heads, given the information you have. You should be willing to make exactly the same bets about them, assuming the person offering you the bet has no more information than you do. However, if you flip each coin once and observe the results, your new probability estimate for next flips are now different.
For example, for the second coin you might have a uniform distribution (ignorance prior) over the set of all possible probabilities. In that case, if you observe a single flip that comes up heads, your probability that the next flip will be heads is now 2/3.
What happens when the committed scorched-earth-defender meets the committed extortionist? Surely a strong precommitment to extortion by a powerful attacker can defeat a weak commitment to scorched earth by a defender?
It seems to me this bears a resemblence to Chicken or something, and that on a large scale we might reasonably expect to see both sets of outcomes.