Murray is only eight years older than Michelle Pfeiffer. It'd be odd for him to play her father. Although I guess if Kang's in the movie, there could be some time travel involved.
My first thought, based just on Reed's description rather than knowledge of comics history, was more along the lines of him being Hope's real father, either Janet's first husband or someone she had an affair with. That could be the thing Janet doesn't want to reveal to Hope.
That was my first thought too, and it made me shudder.
