Assuming that Mary just hung up the phone.
Mary: The guy on the phone had French accent.
Peter: It would be Nathan.
I wonder if it is correct to use "would" in this case, because modal verb "would", unlike will, cannot be used to express the sense of possibility.
Personally, I reckon that "could" should be used OR "would have been", just as:
It would have been Nathan.
To English natives, is "would" usually used in this sense?
your help is immensely valuable.
If he only believes that it's a possibility that it was Nathan, he is more likely to say "Ah, that could be (or have been) Nathan".