One of the most likely consequences is that many banks and other financial institutions will simply avoid the problem by refusing to deal with US citizens effectively making US citizens financial pariahs abroad. Others may also limit the products and services they make available to US citizens. You can open a basic chequing account but not buy units of that high performing hedge fund.
As for Bitcoin I can see:
1) Bitcoin exchanges refusing US Citizens. By the way this is already happening. Ever wonder why Virtex requires Canadian
Citizenship is order to open an account?
4.7 The VirtEx service is not intended to be used by any person under the age of 18 years old or by anyone other than a Canadian citizen. Your use of the VirtEx site shall serve to confirm that you are both 18 years of age or older and a Canadian citizen.
https://www.cavirtex.com/terms2) Ex-pat US citizens being forced to used Bitcoin to avoid what can become an effective worldwide banking blockade against them.