Requesting account names is already common practice: http://www.politico.com/story/2016/12/foreign-travelers-soci.... That does not include passwords, and it's "voluntary". But having filled out US immigration forms a few times (and watched others doing it), the process is quite intimidating and many will be pressured into providing that data. Why else would they? There is no upside to the US gov having that data for me.
With regards to passwords, I don't have numbers, but have seen a few dozen reports over the years without actively looking for them and knowing someone personally to whom it happened (he refused and was allowed entry after a few hours). And whatever is currently discussed would probably include it, considering the San Bernadino case they cite as justification involved information shared with strict privacy setting:
The ESTA form asks for social media accounts (though not passwords, and ostensibly providing the accounts is "optional"): https://esta.cbp.dhs.gov/esta/
With regards to passwords, I don't have numbers, but have seen a few dozen reports over the years without actively looking for them and knowing someone personally to whom it happened (he refused and was allowed entry after a few hours). And whatever is currently discussed would probably include it, considering the San Bernadino case they cite as justification involved information shared with strict privacy setting:
https://www.google.de/search?client=safari&rls=en&q=us+askin...