There are only challenges if he doesn't have the key. If he has the key he should trivially be able to sign anything with it or decrypt anything encrypted to it.

The key could be in a vault inside his secret volcano base. If someone just wires him $ to charter a flight, he can retrieve his millions and share it.

I wonder if the scam he has been running is "front me money to build a supercomputer to bruteforce my passworded wallet containing Satoshi's millions." This would be more convincing if he were actually Satoshi and 'lost' the password....

Is there a reason he hasn't or won't spend some on the original bitcoins to prove his claim?

I don't think spend isn't the proper technical term.

The reason is that he's "too weak", supposedly. The real reason is that he isn't Satoshi.

That's what I thought, but I just wanted to be sure. Thanks!