If I were the interviewer I would be interested in what clarifying questions the candidate would ask and/or how they would highlight parameters and assumptions needed because the question is vague to the point of being unanswerable otherwise.
Proof: suppose there is only 1 infinite stream which is always descending. You will never find a lowest value, so you cannot rewrite the stream "in order".
It's a trivial toy problem. It's not a useful problem to solve. But the question may be there just to get you to think of just this, and to ask questions.
If the input is infinite and unordered and the task is to produce output in order, how do you know when it’s OK to start writing output?
At one job interview I was deliberately given a problem which had no efficient solution. The idea was to find a heuristic which would get close to the optimal solution and run in a reasonable time.