But here's a testable hypothesis for you: ten years from now a Bitcoin will not be convertible into more than $10, if it's reliably convertible into currency at all.
Indeed that is a testable hypothesis, and one I think will be false.
Is it impossible? Couldn't you essentially short by borrowing bitcoins? (e.g. I will borrow 10 bitcoins today, immediately sell them, paying back say 12 bitcoins in three months. That sort of deal). I seriously contemplated such notions during the recent upswing.
I have zero experience with them so that isn't a recommendation, just someone who does it.
In theory, sure. In practice, if no one is lending bitcoins based on the promise to repay more bitcoins later, then, no, you can't short them.
And the fact that one of the selling points of bitcoin is that it doesn't rely on trust might explain why even with a fair amount of money from enthusiasts chasing present bitcoins, there might not be lots of people with bitcoins lending them against a promise of future bitcoins.
Shorting is, as in the normal securities market, a dangerous gambit because the downside is infinitely larger than the upside. But if someone wanted to do it they could.