Will museum be open January 1 2019 with no pass needed.

I walked right in last week in the morning with now pass. Passes are no longer needed but I suggest going earlier because the line can get long as they limit the amount of people that can enter

Yes, but keep in mind all Smithsonian Museums will close January 2nd if the government shutdown continues, and will remain closed until Congress approves a budget.

No I wouldn't count on that and passes are needed early in the morning at least until 1