hanwong, his wife is not a U.S. person, correct? So he has to file "Married, filing separately", and his wife is not required to do anything, correct? I understand why his wife needs a taxpayer identification number (to list on his filing), but why does she need to pay U.S. taxes too?
The following is free information for entertainment purposes solely, does not include any specific tax advise, and cannot be used to avoid penalties...
To determine whether the spouse is or is not a US person is fairly complicated with a long list of tests. The US citizen has the option to file MFS or MFJ, with many advantages and disadvantages to consider.
If the wife is truly a non US person, and he chooses to file MFS, then her income MAY be kept off of his income tax return. As always the true test if this possible scenario of keeping her income off of his US income tax return, contains many many hoops you must jump through.
If your just asking about what the law is, then the above statement is correct. If you care about how a real life situation where a US citizen hasn't filed or paid any taxes in years, lives abroad, has a wife that can afford a 200K car, but your still asking the IRS to give you the best possible tax treatment of your bitcoins so that you can minimize your pound of flesh you have to give up, well I have no comment there.