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".
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.
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?
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.